Avenanthramides Prevent Osteoblast and Osteocyte Apoptosis and Induce Osteoclast Apoptosis in Vitro in an Nrf2-Independent Manner

Asperosaponin VI inhibition of DNMT alleviates GPX4 suppression-mediated osteoblast ferroptosis and diabetic osteoporosis

INTRODUCTION

Diabetic osteoporosis (DOP) is an insidious complication of diabetes with limited therapeutic options. DOP is pathologically associated with various types of regulated cell death, but the precise role of ferroptosis in the process remains poorly understood. Asperosaponin VI (AVI), known for its clinical efficacy in treating bone fractures and osteoporosis, may exert its osteoprotective effects through mechanisms involving ferroptosis, however this has not been established.

OBJECTIVES

This study aimed to investigate the role of AVI in modulating ferroptosis in a mouse model of DOP and to explore the underlying mechanisms.

METHODS

We assessed OP alterations in femurs of DOP-conditioned mice and primary bone cells. We generated a strain of osteoblast-specific Gpx4-deficient mice. A combination of micro-CT, immunohistochemistry, immunofluorescence, methylation-specific PCR (MSP), bisulfite sequencing PCR (BSP), western blotting (WB), and AVI pull-down assays were employed to elucidate the mechanism and therapeutic target of AVI in DOP.

RESULTS

Our findings revealed that femurs from DOP-conditioned mice exhibited significant ferroptosis and suppression of the core anti-ferroptosis factor GPX4, mainly due to hypermethylation of the Gpx4 promoter mediated by DNA methyltransferases DNMT1and DNMT3a. Notably, treatment with AVI effectively reversed the hypermethylation, restored GPX4 expression, and reduced ferroptotic pathologies associated with DOP by inhibiting DNMT1/3a. In primarily-cultured osteoblasts and osteoclasts, AVI alleviated GPX4 suppression and reduced ferroptosis in DOP-conditioned osteoblasts through a mechanism dependent on DNMT inhibition and GPX4 restoration. Importantly, the anti-ferroptotic and osteoprotective effects of AVI were abolished in osteoblastic Gpx4 haplo-deficient mice (Gpx4Ob-/+) or when GPX4 was pharmacologically inactivated with RSL3.

CONCLUSIONS

Our study identifies a pivotal epigenetic ferroptotic pathway that contributes significantly to DOP and uncovers a crucial pharmacological property of AVI that is potentially effective in treating patients with DOP and related osteoporotic disorders.

DNA Methylation-Mediated GPX4 Transcriptional Repression and Osteoblast Ferroptosis Promote Titanium Particle-Induced Osteolysis

Metal wear particles generated by the movement of joint prostheses inevitably lead to aseptic osteolytic damage and ultimately prosthesis loosening, which are aggravated by various types of regulated cell death of bone. Nevertheless, the exact cellular nature and regulatory network underlying osteoferroptosis are poorly understood. Here, we report that titanium particles (TP) induced severe peri-implant osteolysis and ferroptotic changes with concomitant transcriptional repression of a key anti-ferroptosis factor, GPX4, in a mouse model of calvarial osteolysis. GPX4 repression was accompanied by an increase in DNA methyltransferases (DNMTs) 1/3a/3b and hypermethylation of the Gpx4 promoter, which were partly mediated by the transcriptional regulator/co-repressor KLF5 and NCoR. Conversely, treatment with SGI-1027, a DNMT-specific inhibitor, resulted in marked reversal of Gpx4 promoter hypermethylation and GPX4 repression, as well as improvement in ferroptotic osteolysis to a similar extent as with a ferroptosis inhibitor, liproxstatin-1. This suggests that epigenetic GPX4 repression and ferroptosis caused by the increase of DNMT1/3a/3b have a causal influence on TP-induced osteolysis. In cultured primary osteoblasts and osteoclasts, GPX4 repression and ferroptotic changes were observed primarily in osteoblasts that were alleviated by SGI-1027 in a GPX4 inactivation-sensitive manner. Furthermore, we developed a mouse strain with Gpx4 haplodeficiency in osteoblasts (Gpx4 Ob+/-) that exhibited worsened ferroptotic osteolysis in control and TP-treated calvaria and largely abolished the anti-ferroptosis and osteoprotective effects of SGI-1027. Taken together, our results demonstrate that DNMT1/3a/3b elevation, resulting GPX4 repression, and osteoblastic ferroptosis form a critical epigenetic pathway that significantly contributes to TP-induced osteolysis, and that targeting DNMT aberration and the associated osteoferroptosis could be a potential strategy to prevent or slow down prosthesis-related osteolytic complications.

Orexin-A Reverse Bone Mass Loss Induced by Chronic Intermittent Hypoxia Through OX1R-Nrf2/HIF-1α Pathway

Background

Recent studies suggest that there is a potential connection between obstructive sleep apnea (OSA) and osteoporosis through dysregulation of bone metabolism. Orexin-A, a neuroprotective peptide secreted by the hypothalamus, is at a lower level in the plasma of OSA patients, which regulates appetite, energy expenditure and sleep-wake states. However, the protective effect of orexin-A on bone metabolism in OSA is unclear.

Purpose

To investigate whether the activation of OX1R by orexin-A can reverse bone mass loss induced by chronic intermittent hypoxia (CIH).

Methods

Mice were randomly divided into the normoxia group and CIH group. Within the CIH or normoxia groups, treatment groups were given a subcutaneous injection of either orexin-A or saline vehicle once every day for 4 weeks and then femurs were removed for micro-CT scans. Histology and immunohistochemical staining were performed to observe and calculate the changes in femurs as a result of hypoxia. Cell immunofluorescence and immunohistochemical staining were used to detect the expression of orexin receptors in MC3T3-E1 cells or in bones. CCK-8 assay, ALP assay kit and alizarin red staining were used to detect the viability, alkaline phosphatase (ALP) activity, and capacity of mineralization, respectively. The effect of orexin-A on osteogenic differentiation of MC3T3-E1 cells was evaluated using qRT-PCR, Western blot and cell staining.

Results

CIH led to a decrease in the amount and density of trabecular bone, downregulated OCN expression while increasing osteoclast numbers in femurs and inhibited the expression of RUNX2, OSX, OPN and Nrf2 in MC3T3-E1 cells. Orexin-A treatment alleviated these CIH-induced effects by combining to OX1R. The level of HIF-1α was elevated both in CIH and orexin-A treatment groups.

Conclusion

CIH environment inhibits osteogenesis and orexin-A can reverse bone mass loss induced by CIH through OX1R-Nrf2/HIF-1α pathway.

Inhibitory Mechanism of Advanced Glycation End-Product Formation by Avenanthramides Derived from Oats through Scavenging the Intermediates

As a special polyphenolic compound in oats, the physiological function of oat avenanthramides (AVAs) drives a variety of biological activities, and plays an important role in the prevention and treatment of common chronic diseases. In this study, the optimum extraction conditions and structural identification of AVAs from oats was studied. The inhibitory effect of AVAs from oats on advanced glycation end-products (AGEs) in a glucose–casein simulation system was evaluated, and this revealed dose-dependent inhibitory effects. The trapping capacity of AVAs to the α-dicarbonyl compounds of AGE intermediate products was determined by HPLC–MS/MS, and the results indicate that AVA 2c, AVA 2p, and AVA 2f exhibited the ability to capture α-dicarbonyl compounds. More importantly, AVA 2f was found to be more efficient than AVA 2p at inhibiting superoxide anion radical (O₂⁻), hydroxyl radical (OH), and singlet oxygen (¹O₂) radical generation, which may be the main reason that AVA 2f was more efficient than AVA 2p in AGE inhibition. Thus, this research presents a promising application of AVAs from oats in inhibiting the food-borne AGEs formed in food processing.

Genetic diversity in nutritional composition of oat (Avena sativa L.) germplasm reported from Pakistan

In the present study, 30 potential germplasm of oat (Avena sativa L.) were subjected to proximate, elemental, and HPLC analysis to provide a scientific basis to genetic diversity present among them. The extracts of the selected germplasms were also evaluated for their antioxidant potentials through DPPH and ABTS assays. Proximate analysis showed protein contents to be in the range 8.35–17.72% with the highest protein contents in the accession line 22,365 (17.72 ± 0.38%). The genotype-725 showed the highest carbohydrate, and dry matter (53.35 ± 0.01 and 93.50 ± 0.07% respectively) contents whereas, the germplasm-830 contained the highest fat (7.88 ± 0.12%) contents while the highest moisture contents were there in germplasm-22348 (11.95 ± 0.06%). The crude fiber contents (19.67 ± 0.19%) were found high in germplasm-832. The mentioned contents were also correlated to each other where a negative (−0.431*) correlation was noted for crude protein and carbohydrate while ash content to crude protein has a positive (0.38*) correlation. A positive and a negative correlation were there in Crude fats/crude protein (0.30*) and crude fats/moisture contents (−0.39*) respectively. Principal component analysis showed an Eigenvalue of 0.76 with a total variation of 85.01% when applied to proximate components. Based on cluster analysis to proximate composition all the oat germplasms were divided into 5 sub-clusters, where accession numbers 769 and 817 were found to be the most diverse genotypes. The elemental analysis confirmed the presence of magnesium (2.89–7.62 mg/L), sodium (3.71–8.03 mg/L), manganese (0.93–3.71 mg/L), copper (0.35–3.36 mg/L), iron (2.15–6.82 mg/L), zinc (1.30–3.37 mg/L), chromium (0.37–3.34 mg/L), and potassium (50.70–59.60 mg/L) in the selected germplasms. Principal component analysis for elemental composition showed the total variation of 73.75% with the Eigenvalue of 0.97. Cluster analysis on an elemental basis divided all the oat germplasms into 7 sub-clusters where accession numbers 769 and 22,350 were found to be the most diverse germplasm. Phytochemical analysis performed through HPLC resulted in the identification of nine possible compounds (malic acid, epigallocatechin gallate, quercetin, morin, ellagic acid, catechin hydrate, rutin, pyrogallol, and mandelic acid) in various germplasm of oat. A concentration-dependent antioxidant response was recorded when extracts were tested as an inhibitor of DPPH and ABTS free radicals. The results revealed that oat grains are a good source of nutrients, minerals, and phytochemicals that can be used as nutraceuticals and as food. The genetic differences revealed that this plant can be grown under varied environmental conditions.

Avenanthramide C from Oats Protects Pyroptosis through Dependent ROS-Induced Mitochondrial Damage by PI3K Ubiquitination and Phosphorylation in Pediatric Pneumonia

Oat containing rich β-glucan, polyphenols, flavonoids, saponins, alkaloids, and other substances shows good biological activities. Therefore, the present study aimed to uncover the possible mechanism and therapeutic effect of Avenanthramide C in lessening inflammatory responses in pediatric pneumonia. Pediatric pneumonia was induced by liposaccharide (LPS) for vivo model and vitro model. Macrophage was performed to determine the mechanism and effects of Avenanthramide C in pediatric pneumonia. NLRP3 activity participated in the effects of Avenanthramide C in pediatric pneumonia. Avenanthramide C induced p-PI3K and p-Akt expressions and reduced ubiquitination of PI3K expression in pediatric pneumonia. On the other hand, Avenanthramide C integrated serine at 821 sites of the PI3K protein function. Avenanthramide C reduced ROS (reactive oxygen species)-induced mitochondrial damage by PI3K/AKT function in a model of pediatric pneumonia. Avenanthramide C protects pyroptosis in a model of pediatric pneumonia by PI3K/AKT/Nrf2/ROS signaling. Taken together, our results demonstrated that Avenanthramide C protects pyroptosis through dependent ROS-induced mitochondrial damage by PI3K ubiquitination and phosphorylation in a model of pediatric pneumonia, suggesting its potential use for the treatment of pediatric pneumonia and other inflammatory diseases.

The Progress of Nomenclature, Structure, Metabolism, and Bioactivities of Oat Novel Phytochemical: Avenanthramides

Oats are among the most commonly consumed whole grains and are widely grown worldwide, and they contain numerous nutrients, including proteins, lipids, vitamins, minerals, β-glucan, and unique phytochemical polyphenol avenanthramides (Avns). Recent studies have indicated that Avns play essential roles in mediating the health benefits of oats. This review systemically summarized the nomenclature and structures of Avns, effect of germination on promoting Avns production, and in vivo metabolites produced after Avns consumption. The classical functions and novel potential bioactivities of Avns were further elucidated. The classical functions of Avns in cancer prevention, antioxidative response, anti-inflammatory reaction, and maintaining muscle health were expounded, and the internal mechanisms of these functions were analyzed. The potential novel bioactivities of Avns in modulating gut microbiota, alleviating obesity, and preventing chronic diseases, such as atherosclerosis and osteoporosis, were further revealed. This review may provide new prospects and directions for the development and utilization of oat Avns.

Diphlorethohydroxycamalol isolated from Ishige okamurae prevents H2O2-induced oxidative damage via BMP2/Runx2 signaling in osteoblastic MC3T3-E1 cells

Accumulating evidence has shown an association between osteoporosis and oxidative damage. In the present study, the protective effects of diphlorethohydroxycarmalol (DPHC) isolated from the brown algae Ishige okamurae against H2O2-induced oxidative damage via bone morphogenetic protein 2 (BMP2)/ runt-related transcription factor 2 (Runx2) signaling were investigated using MC3T3-E1 osteoblastic cells. DPHC counteracted the reduction in cell viability caused by H2O2 exposure and protected against H2O2-induced dysfunction, demonstrated by improved cellular alkaline phosphatase (ALP) activity and calcium deposition. In addition, treatment with 0.05-0.2 mM DPHC elevated the protein expression of osteoblast differentiation factors type 1 collagen, ALP, p-Smad1/5, Osterix, BMP2, and Runx2, in response to H2O2-induced oxidative damage. Importantly, DPHC decreased the expression levels of receptor activator of nuclear factor kappa-B ligand, which promotes bone resorption, and inhibited the H2O2-induced generation of reactive oxygen species. Taken together, the results suggest that DPHC counteracts the effects of oxidative stress in osteoblastic cells and has the potential to be effective in preventing and alleviating osteoporosis.

Oat polyphenol avenanthramide-2c confers protection from oxidative stress by regulating the Nrf2-ARE signaling pathway in PC12 cells

Accumulating evidence has demonstrated that cellular antioxidant systems play essential roles in retarding oxidative stress-related diseases, such as Parkinson's disease. Because nuclear factor erythroid 2-related factor 2 (Nrf2) is a chief regulator of cellular antioxidant systems, small molecules with Nrf2-activating ability may be promising neuroprotective agents. Avenanthramide-2c (Aven-2c), avenanthramide-2f (Aven-2f) and avenanthramide-2p (Aven-2p) are the most abundant avenanthramides in oats, and they have been documented to possess multiple pharmacological benefits. In this work, we synthesized these three compounds and evaluated their cytoprotective effect against oxidative stress-induced PC12 cell injuries. Aven-2c displayed the best protective potency among them. Aven-2c conferred protection on PC12 cells by scavenging free radicals and activating the Nrf2-ARE signaling pathway. Pretreatment of PC12 cells with Aven-2c efficiently enhanced Nrf2 nuclear accumulation and evoked the expression of a set of cytoprotective molecules. The mechanistic study also supports that Nrf2 activation is the molecular basis for the cellular action of Aven-2c. Collectively, this study demonstrates that Aven-2c is a potent Nrf2 agonist, shedding light on the potential usage of Aven-2c in the treatment of neuroprotective diseases.

Nrf2 epigenetic derepression induced by running exercise protects against osteoporosis

Osteoporosis (OP) is a common skeletal disease involving low bone mineral density (BMD) that often leads to fragility fracture, and its development is affected by multiple cellular pathologies and associated with marked epigenetic alterations of osteogenic genes. Proper physical exercise is beneficial for bone health and OP and reportedly possesses epigenetic modulating capacities; however, whether the protective effects of exercise on OP involve epigenetic mechanisms is unclear. Here, we report that epigenetic derepression of nuclear factor erythroid derived 2-related factor-2 (Nrf2), a master regulator of oxidative stress critically involved in the pathogenesis of OP, mediates the significant osteoprotective effects of running exercise (RE) in a mouse model of OP induced by ovariectomy. We showed that Nrf2 gene knockout (Nfe2l2^-/-) ovariectomized mice displayed a worse BMD reduction than the controls, identifying Nrf2 as a critical antiosteoporotic factor. Further, femoral Nrf2 was markedly repressed with concomitant DNA methyltransferase (Dnmt) 1/Dnmt3a/Dnmt3b elevations and Nrf2 promoter hypermethylation in both patients with OP and ovariectomized mice. However, daily 1-h treadmill RE significantly corrected epigenetic alterations, recovered Nrf2 loss and improved the femur bone mass and trabecular microstructure. Consistently, RE also normalized the adverse expression of major osteogenic factors, including osteoblast/osteoclast markers, Nrf2 downstream antioxidant enzymes and proinflammatory cytokines. More importantly, the RE-conferred osteoprotective effects observed in the wild-type control mice were largely abolished in the Nfe2l2^-/- mice. Thus, Nrf2 repression due to aberrant Dnmt elevation and subsequent Nrf2 promoter hypermethylation is likely an important epigenetic feature of the pathogenesis of OP, and Nrf2 derepression is essential for the antiosteoporotic effects of RE.

Wheat, Barley, and Oat Breeding for Health Benefit Components in Grain

Cereal grains provide half of the calories consumed by humans. In addition, they contain important compounds beneficial for health. During the last years, a broad spectrum of new cereal grain-derived products for dietary purposes emerged on the global food market. Special breeding programs aimed at cultivars utilizable for these new products have been launched for both the main sources of staple foods (such as rice, wheat, and maize) and other cereal crops (oat, barley, sorghum, millet, etc.). The breeding paradigm has been switched from traditional grain quality indicators (for example, high breadmaking quality and protein content for common wheat or content of protein, lysine, and starch for barley and oat) to more specialized ones (high content of bioactive compounds, vitamins, dietary fibers, and oils, etc.). To enrich cereal grain with functional components while growing plants in contrast to the post-harvesting improvement of staple foods with natural and synthetic additives, the new breeding programs need a source of genes for the improvement of the content of health benefit components in grain. The current review aims to consider current trends and achievements in wheat, barley, and oat breeding for health-benefiting components. The sources of these valuable genes are plant genetic resources deposited in genebanks: landraces, rare crop species, or even wild relatives of cultivated plants. Traditional plant breeding approaches supplemented with marker-assisted selection and genetic editing, as well as high-throughput chemotyping techniques, are exploited to speed up the breeding for the desired genotуpes. Biochemical and genetic bases for the enrichment of the grain of modern cereal crop cultivars with micronutrients, oils, phenolics, and other compounds are discussed, and certain cases of contributions to special health-improving diets are summarized. Correlations between the content of certain bioactive compounds and the resistance to diseases or tolerance to certain abiotic stressors suggest that breeding programs aimed at raising the levels of health-benefiting components in cereal grain might at the same time match the task of developing cultivars adapted to unfavorable environmental conditions.

Adverse Impact of Heavy Metals on Bone Cells and Bone Metabolism Dependently and Independently through Anemia

Mounting evidence is revealing that heavy metals can incur disordered bone homeostasis, leading to the development of degenerative bone diseases, including osteoporosis, osteoarthritis, degenerative disk disease, and osteomalacia. Meanwhile, heavy metal-induced anemia has been found to be intertwined with degenerative bone diseases. However, the relationship and interplay among these adverse outcomes remain elusive. Thus, it is of importance to shed light on the modes of action (MOAs) and adverse outcome pathways (AOPs) responsible for degenerative bone diseases and anemia under exposure to heavy metals. In the current Review, the epidemiological and experimental findings are recapitulated to interrogate the contributions of heavy metals to degenerative bone disease development which may be attributable dependently and independently to anemia. A few likely mechanisms are postulated for anemia-independent degenerative bone diseases, including dysregulated osteogenesis and osteoblastogenesis, imbalanced bone formation and resorption, and disturbed homeostasis of essential trace elements. By contrast, remodeled bone microarchitecture, inhibited erythropoietin production, and disordered iron homeostasis are speculated to account for anemia-associated degenerative bone disorders upon heavy metal exposure. Together, this Review aims to elaborate available literature to fill in the knowledge gaps in understanding the detrimental effects of heavy metals on bone cells and bone homeostasis through different perspectives.

Two new secondary metabolites isolated from Avena sativa L. (Oat) seedlings and their effects on osteoblast differentiation

Seedlings of natural crops are valuable sources of pharmacologically active phytochemicals. In this study, we aimed to identify new active secondary metabolites in Avena sativa L. (oat) seedlings. Two new compounds, avenafuranol (1) and diosgenoside (2), along with eight known compounds (3-10) were isolated from the A. sativa L. seedlings. Their chemical structures were elucidated via 1D and 2D NMR spectroscopy, high-resolution ESIMS, IR spectroscopy, optical rotation analysis, and comparisons with the reported literature. The effect of each isolated compound on alkaline phosphatase (ALP) activity for osteoblast differentiation induced by bone morphogenetic protein-2 (BMP-2) was investigated using the C2C12 immortal mouse myoblast cell line. Compounds 1, 4, 6, 8, and 9 induced dose-dependent increases in ALP expression relative to ALP expression in cells treated with only BMP-2, and no cytotoxicity was observed. These results suggest that A. sativa L. seedlings are a natural source of compounds that may be useful for preventing bone disorders.

Curcumin Protects Osteoblasts From Oxidative Stress-Induced Dysfunction via GSK3β-Nrf2 Signaling Pathway

Osteoblasts dysfunction, induced by oxidative stress (OS), is one of major pathological mechanisms for osteoporosis. Curcumin (Cur), a bioactive antioxidant compound, isolated from Curcumin longa L, was regarded as a strong reactive oxygen species (ROS) scavenger. However, it remains unveiled whether Cur can prevent osteoblasts from OS-induced dysfunction. To approach this question, we adopted a well-established OS model to investigate the preventive effect of Cur on osteoblasts dysfunction by measuring intracellular ROS production, cell viability, apoptosis rate and osteoblastogenesis markers. We showed that the pretreatment of Cur could significantly antagonize OS so as to suppress endogenous ROS production, maintain osteoblasts viability and promote osteoblastogenesis. Inhibiting Glycogen synthase kinase (GSK3β) and activating nuclear factor erythroid 2 related factor 2 (Nrf2) could significantly antagonize the destructive effects of OS, which indicated the critical role of GSK3β-Nrf2 signaling. Furthermore, Cur also abolished the suppressive effects of OS on GSK3β-Nrf2 signaling pathway. Our findings demonstrated that Cur could protect osteoblasts against OS-induced dysfunction via GSK3β-Nrf2 signaling and provide a promising way for osteoporosis treatment.

MiR-27b-3p exerts tumor suppressor effects in esophageal squamous cell carcinoma by targeting Nrf2

MiR-27b-3p has been reported to function as tumor suppressor in several tumors, including breast cancer and lung cancer. Recently, miR-27b-3p has been identified to be significantly down-regulated in esophageal cancer. However, the clinical significance and biological role of miR-27b-3p in esophageal squamous cell carcinoma (ESCC) still remain unclear. In this study, the expression levels of miR-27b-3p were significantly reduced in ESCC clinical tissues and ESCC cell lines (EC97069 and TE-1). Moreover, down-regulated expression of miR-27b-3p was associated with poor cell differentiation, TNM stage and lymph node metastasis. Specially, overexpression of miR-27b-3p significantly suppressed cell proliferation, migration and invasion in vitro using CCK-8 and transwell assays. Targetscan bioinformatics predictions and luciferase reporter assay confirmed that nuclear factor erythroid 2-related factor 2 (NFE2L2, Nrf2) was a direct target gene of miR-27b-3p. Nrf2 expression was significantly increased in ESCC tissues compared with adjacent tissues. Up-regulated expression of Nrf2 was correlated with TNM stage and lymph node metastasis. Functionally, knockdown of Nrf2 exhibited similar effects to overexpression of miR-27b-3p. Higher expression of ZO-1, E-cadherin and lower expression of N-cadherin, Vimentin and Claudin-1 were observed after miR-27b-3p overexpression of Nrf2 knockdown. Rescue experiments proved that miR-27b-3p suppressed cell proliferation, migration, invasion and epithelial to mesenchymal transition (EMT) via suppression of Nrf2. Taken together, the newly identified miR-27b-3p/Nrf2 axis might represent a new candidate therapeutic target for ESCC treatment.

Effects of irisin on osteoblast apoptosis and osteoporosis in postmenopausal osteoporosis rats through upregulating Nrf2 and inhibiting NLRP3 inflammasome

The nuclear factor E2-related factor 2 (Nrf2)/NLR family, pyrin domain containing protein 3 (NLRP3) plays an important role in osteoporosis (OP), so the effects of irisin on postmenopausal OP rats and osteoblast apoptosis through Nrf2/NLRP3 were explored in the present study. A total of 45 specific pathogen-free Sprague-Dawley rats were selected and divided into OP model group (OP group, n=15), 1 mmol/l irisin treatment group (irisin group, n=15) and normal control group (control group, n=15). After the trial period, the content of serum ALP was detected, the levels of tumor necrosis factor-α (TNF-α) in the serum and bone tissues were observed via ELISA, and the bone microstructure was observed via CT. Osteoblast apoptosis was determined through TUNEL assay, the content of apoptosis genes caspase-3 and Bcl-2, and key genes in Runt-related transcription factor 2 (Runx2), osteocalcin (OC), Nrf2 and NLRP3 was detected via RT-PCR. The protein expression of Bcl-2, Nrf2 and NLRP3 was determined via western blotting. The serum ALP level was increased in OP group compared with that in control group (P<0.05), while it declined in the irisin group. The content of TNF-α and interleukin-6 (IL-6) was significantly higher in OP group, while the content in the irisin group was close to that in the control group. The trabecular thickness, number and bone mineral density in the irisin group were all obviously larger and higher, respectively, than those in the OP group. The mRNA expression of Runx2, OC, Bcl-2 and Nrf2 in the irisin group were obviously higher (P<0.05), while that of caspase-3 and NLRP3 showed the opposite trends. The protein expression of Bcl-2 and Nrf2 in the irisin group was remarkably higher than those in the OP group, while that of NLRP3 was the opposite. irisin can upregulate Nrf2, inhibit NLRP3 inflammasome and lower the content of inflammatory factors, thereby suppressing osteoblast apoptosis in postmenopausal OP rats and reducing the incidence of postmenopausal OP.

Inhibition of JNK and activation of the AMPK-Nrf2 axis by corosolic acid suppress osteolysis and oxidative stress

The intracellular reactive oxygen species contribute to RANKL-induced osteoclastogenesis and osteolysis. Nuclear factor-erythroid 2-related factor 2 (Nrf2), a redox-sensitive transcription factor, is critical in the cellular defense against oxidative stress by induction of antioxidants and cytoprotective enzymes. In the current study, it was first demonstrated that RANKL-induced osteoclastogenesis and hydroxylapatite resorption were suppressed by Corosolic acid (CA) via inhibiting p-JNK and activating p-AMPK. Meanwhile, p-65, p-38, Akt, and GSK-3β were partly inhibited during the treatment of CA. Osteoclastogenesis related genes, including NFATc1, c-fos, cathepsin K, and CTR were down-regulated by CA as well. Furthermore, the intracellular oxidative stress of CA-treated osteoclasts was dramatically decreased and Nrf2 was translocated into the nucleus to activate antioxidants including HO-1, NQO-1, and GCLC by CA. The LPS-induced mice calvarial osteolysis model was established for the in vivo investigation. Micro-CT morphometric analysis revealed that the treatment of CA restored LPS-induced bone loss and formation of osteoclasts. Besides, p-p65 and p-JNK were activated in the LPS group but inhibited by CA in vivo. The treatment of CA also activated p-AMPK during its attenuating LPS-induced osteolysis. Conclusively, CA effectively protects against LPS-induced osteolysis by suppressing osteoclastogenesis and oxidative stress through the inhibition of the JNK and activation of the AMPK-Nrf2 axis.

Glycyrrhizin Suppresses RANKL-Induced Osteoclastogenesis and Oxidative Stress Through Inhibiting NF-κB and MAPK and Activating AMPK/Nrf2

The treatment for osteoporosis involves inhibiting bone resorption and osteoclastogenesis. Glycyrrhizin (GLY) is a triterpenoid saponin glycoside known to be as the most medically efficacious component of the licorice plant. It has strong anti-inflammatory, antioxidant, and antitumor properties. We investigated the effect of GLY on osteoclastogenesis, bone resorption, and intracellular oxidative stress and its molecular mechanisms. In vitro osteoclastogenesis assays were performed using bone marrow monocytes with and without glycyrrhizin. We also evaluated the effects of glycyrrhizin on the secretion of TNF-α, IL-1β, and IL-6 in LPS-stimulated RAW 264.7 cells using ELISA. The effects of glycyrrhizin on the expression of osteoclast-related genes, such as Nfatc1, c-fos, Trap, and cathepsin K (CK), were investigated by RT-PCR. Intracellular reactive oxygen species (ROS) were detected in receptor activator of nuclear factor kappa-Β ligand (RANKL)-stimulated osteoclasts in the presence and absence of glycyrrhizin. During the inhibition of osteoclastogenesis by glycyrrhizin, phosphorylation of AMPK, Nrf2, NF-κB, and MAPK was analyzed using western blotting. Our results showed that glycyrrhizin significantly inhibited RANKL-induced osteoclastogenesis, downregulated the expression of NFATc1, c-fos, TRAP, CK, DC-STAMP, and OSCAR, and inhibited p65, p38, and JNK. Glycyrrhizin was found to significantly decrease the secretion of inflammatory cytokines (TNF-α, IL-1β, and IL-6). Additionally, glycyrrhizin reduced the formation of ROS in osteoclasts by inducing AMPK phosphorylation and nuclear transfer of NRF2, resulting in an upregulation of antioxidant enzymes, such as HO-1, NQO-1, and GCLC. In summary, we found that glycyrrhizin inhibited RANKL-induced osteoclastogenesis. It was also indicated that glycyrrhizin could reduce oxidative stress by inhibiting the MAPK and NF-κB pathways and activating the AMPK/NRF2 signaling. Therefore, glycyrrhizin may be used as an effective therapeutic agent against osteoporosis and bone resorption.

Glucagon-like peptide 2 decreases osteoclasts by stimulating apoptosis dependent on nitric oxide synthase

OBJECTIVES

Glucagon-like peptide 2 (GLP2) is involved in the regulation of energy absorption and metabolism. Despite the importance of the GLP2 signalling mechanisms on osteoclast, little has been studied on how GLP2 works during osteoclastogenesis.

MATERIALS AND METHODS

RAW264.7 cells were infected with rLV-Green-GLP2. The induction of osteoclasts was performed by RANKL. TRAP were detected by RT-PCR, Western blotting and staining. Total nitric oxide and total NOS activity were measured. Cells apoptosis was detected by Hoest33258 and Annix V staining. Animal test, chromatin immunoprecipitation (CHIP), co-immunoprecipitation(IP) and luciferase reporter assay were also performed.

RESULTS

We indicate that GLP2 is associated with osteoporosis-related factors in aged rats, including BALP, TRAP, IL6, TNFα, Nitric Oxide (NO), iNOS, calcitonin and occludin. Moreover, GLP2 is demonstrated to result in negative action during proliferation of tartrate-resistant acid phosphatase-positive (TRAP+) osteoclasts. Furthermore, GLP2 decreases osteoclasts induced from monocyte/macrophage cells RAW264.7 as well as the serum TRAP activity in aged rats. Mechanistic investigations reveal GLP2 enhances the expression of iNOS through stimulating the activity of TGFβ-Smad2/3 signalling in osteoclasts. In particular, inhibition of TGFβ fully abrogates this function of GLP2 in osteoclasts. Strikingly, overexpression of GLP2 significantly increases the product of nitric oxide via iNOS which promotes apoptosis of osteoclasts by decreasing bcl2 or increasing caspase3. Thereby, the ability of GLP2 to regulate apoptosis depends on TGFβ-Smad2/3-iNOS-NO signalling pathway since total NOS inhibitor L-NMMA specifically inhibits the actions by GLP2.

CONCLUSIONS

GLP2 induces apoptosis via TGFβ-Smad2/3 signalling, which contributes to the inhibition of the proliferation of osteoclasts and which may provide potential therapeutic targets for the treatment of osteoporosis.

Gastrodin protects MC3T3-E1 osteoblasts from dexamethasone-induced cellular dysfunction and promotes bone formation via induction of the NRF2 signaling pathway

Glucocorticoid (GC)-induced osteoporosis (GIO) is one of the most common secondary and iatrogenic forms of osteoporosis. GCs are widely used in clinical therapy and play a key role in the normal regulation of bone remodeling. However, the prolonged and high-dose administration of GCs results in the occurrence of osteoporosis, which is partially due to the dysfunction and apoptosis of osteoblasts and osteocytes. The aim of the present study was to investigate the effects of gastrodin, a natural bioactive compound isolated from the traditional Chinese herbal agent Gastrodia elata, on GC-treated MC3T3‑E1 murine osteoblastic cells. MC3T3‑E1 cells were exposed to dexamethasone (DEX), with or without gastrodin pretreatment, and cell viability was measured by the cell counting kit-8 (CCK-8) assay. Quantitative polymerase chain reaction analysis was performed to evaluate osteogenic gene expression, and cellular alkaline phosphatase (ALP) activity was measured as well. Alizarin Red staining of calcium deposits was found to reflect the degree of osteoblast maturity. Western blotting was performed to determine the expression of osteogenic and adipogenic differentiation key proteins, as well as nuclear factor-like 2 (NRF2) pathway‑related proteins. Annexin V-fluorescein isothiocyanate̸propidium iodide flow cytometric analysis was performed to determine osteoblast apoptosis. JC-1 staining was used to detect the changes of the mitochondrial membrane potential in cells. The results revealed that gastrodin prevented the decrease in cell viability caused by DEX-induced MC3T3‑E1 cell dysfunction, and that groups pretreated with gastrodin exhibited higher mRNA levels of osteogenic genes, such as Runx2, osterix, bone morphogenetic protein-2 and osteocalcin. Furthermore, treatment with both DEX and gastrodin was associated with increased ALP activity in MC3T3-E1 cells, as well as more calcium deposits, compared with cells treated with DEX alone. In addition, gastrodin increased osteogenic key marker protein Runx2 while activating NRF2 and downstream effector protein expression. Therefore, gastrodin may have the potential to reduce DEX-induced cell apoptosis and increase the mitochondrial membrane potential against DEX. These results demonstrated that gastrodin was able to prevent and/or delay DEX‑induced osteoporosis by improving osteoblast function, and these protective effects were verified in an animal model.

Berberine alleviates oxidative stress in rats with osteoporosis through receptor activator of NF-kB/receptor activator of NF-kB ligand/osteoprotegerin (RANK/RANKL/OPG) pathway

Previous studies suggested that oxidative stress is related to the onset and development of osteoporosis. Moreover, it was demonstrated that berberine has a protective effect against oxidative stress-induced injuries. In this study, we aimed to investigate the effect and mechanism of action of berberine on rats with induced osteoporosis. Sixty 8-week-old female Wistar rats were randomly divided into the following 6 groups: control saline-treated, osteoporosis saline-treated, 3 osteoporosis berberine-treated groups (Ber 5, 10, and 20 mg/kg/body weight, respectively), and osteoporosis alendronate-treated (ALD) group. Osteoporosis was induced by bilateral ovariectomy. All treatments were performed for 8 weeks. The bone mineral density (BMD), serum alkaline phosphatase (ALP), osteocalcin, calcium, phosphorus, superoxide dismutase (SOD), methylenedioxyamphetamine (MDA), and glutathione peroxidase (GSH-Px) level was determined in the rat femur tissue. The gene and protein expression of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-B ligand (RANKL) was analyzed by quantitative reverse transcription PCR and Western blot, respectively. The BMD, SOD and GSH⁃Px levels, and the expression of OPG were significantly lower in osteoporosis compared to control group (all p < 0.05). The serum levels of osteocalcin, ALP, and MDA, and the expression of RANKL were significantly higher in osteoporosis compared to control group (all p < 0.05). Berberine, especially the high doses of berberine, effectively increased SOD, GSH⁃Px, and OPG levels as well as decreased serum osteocalcin, ALP, MDA and RANKL levels in berberine-treated osteoporosis groups (all p < 0.05). To conclude, oxidative stress may promote the development of osteoporosis in rats through the RANK/RANKL/OPG pathway. The antioxidative effect of berberine reduces the development of osteoporosis in rats to some extent.

Ethnobotanic, Ethnopharmacologic Aspects and New Phytochemical Insights into Moroccan Argan Fruits

This review summarizes available data on argan fruit botany, geographical distribution, traditional uses, environmental interest, socioeconomic role, phytochemistry, as well as health beneficial effects and examination of future prospects. In particular, ethnomedical uses of argan fruits are carried out throughout Morocco where it has been used against various diseases. Different classes of bioactive compounds have been characterized including essential oils, fatty acids, triacylglycerols, flavonoids and their newly reported acylglycosyl derivatives, monophenols, phenolic acids, cinnamic acids, saponins, triterpenes, phytosterols, ubiquinone, melatonin, new aminophenols along with vitamin E among other secondary metabolites. The latter have already shown a wide spectrum of in vitro, and ex vivo biologicalactivities including antioxidant, anti-inflammatory, anti-diabetic, antihypertensive, anti-hypercholesterolemia, analgesic, antimicrobial, molluscicidal anti-nociceptive and anticancer potential. Argan flesh (pulp) contains a broad spectrum of polyphenolic compounds which may have utility for incorporation into nutraceuticals and cosmeceuticals relevant to the food, cosmetic and health industries. Further research is recommended, especially on the health beneficial effects of the aminophenols.

Common Chemical Inductors of Replication Stress: Focus on Cell-Based Studies

DNA replication is a highly demanding process regarding the energy and material supply and must be precisely regulated, involving multiple cellular feedbacks. The slowing down or stalling of DNA synthesis and/or replication forks is referred to as replication stress (RS). Owing to the complexity and requirements of replication, a plethora of factors may interfere and challenge the genome stability, cell survival or affect the whole organism. This review outlines chemical compounds that are known inducers of RS and commonly used in laboratory research. These compounds act on replication by direct interaction with DNA causing DNA crosslinks and bulky lesions (cisplatin), chemical interference with the metabolism of deoxyribonucleotide triphosphates (hydroxyurea), direct inhibition of the activity of replicative DNA polymerases (aphidicolin) and interference with enzymes dealing with topological DNA stress (camptothecin, etoposide). As a variety of mechanisms can induce RS, the responses of mammalian cells also vary. Here, we review the activity and mechanism of action of these compounds based on recent knowledge, accompanied by examples of induced phenotypes, cellular readouts and commonly used doses.