Dimethyloxaloylglycine increases the bone healing capacity of adipose-derived stem cells by promoting osteogenic differentiation and angiogenic potential

Association between dietary copper intake and bone mineral density in children and adolescents aged 8-19 years: A cross-sectional study

PURPOSE

Some studies showed the possible role of copper intake on bone mineral density (BMD) in adults or the elderly, but the association remained uncertain in children and adolescents. Our research explored the association between copper intake and BMD in individuals aged 8-19 years from the National Health and Nutrition Examination Survey (NHANES) 2011-2016.

METHODS

In the present study, 6,965 individuals aged 8-19 (mean age 13.18 ± 3.38 years) were enrolled from the NHANES 2011-2016. Copper intake was evaluated by averaging two 24-hour copper dietary intake recalls. Multivariate linear regression analyses were used to explore the association between copper intake and total BMD, subtotal BMD, and total spine BMD in children and adolescents. Stratified analyses and interaction tests were performed by age, gender, and race.

RESULTS

Participants of the higher quartile of copper intake were more likely to be older, men, Non-Hispanic White, and Other Hispanic. They have higher values of poverty income ratio (PIR), serum phosphorus, blood urea nitrogen, serum vitamin D, and BMD and lower values of body mass index (BMI), cholesterol, total protein, and serum cotinine. In the fully adjusted model, we found positive associations between copper intake and total BMD (β = 0.013, 95CI: 0.006, 0.019)), subtotal BMD (β = 0.020, 95CI: 0.015, 0.024), and total spine BMD (β = 0.014, 95CI: 0.009, 0.019). Stratified analyses showed that the association was stronger in men, individuals aged 14-19, Non-Hispanic White, and Other Hispanic.

CONCLUSIONS

Our study suggests that copper intake is positively associated with BMD in U.S. children and adolescents. The study emphasizes the role of copper intake on bone health in the early stages of life. However, more investigations are needed to verify our findings and their underlying mechanisms.

Is Copper Still Safe for Us? What Do We Know and What Are the Latest Literature Statements?

Copper (Cu) is a precious metal and one of the three most abundant trace elements in the body (50-120 mg). It is involved in a large number of cellular mechanisms and pathways and is an essential cofactor in the function of cellular enzymes. Both its excess and deficiency may be harmful for many diseases. Even small changes in Cu concentration may be associated with significant toxicity. Consequently, it can be damaging to any organ or tissue in our body, beginning with harmful effects already at the molecular level and then affecting the degradation of individual tissues/organs and the slow development of many diseases, such as those of the immunological system, skeletal system, circulatory system, nervous system, digestive system, respiratory system, reproductive system, and skin. The main purpose of this article is to review the literature with regard to both the healthiness and toxicity of copper to the human body. A secondary objective is to show its widespread use and sources, including in food and common materials in contact with humans. Its biological half-life from diet is estimated to range from 13 to 33 days. The retention or bioavailability of copper from the diet is influenced by several factors, such as age, amount and form of copper in the diet, lifestyle, and genetic background. The upper limit of normal in serum in healthy adults is approximately 1.5 mg Cu/L, while the safe upper limit of average intake is set at 10-12 mg/day, the reference limit at 0.9 mg/day, and the minimum limit at 0.6-0.7 mg/day. Cu is essential, and in the optimal dose, it provides antioxidant defense, while its deficiency reduces the body's ability to cope with oxidative stress. The development of civilization and the constant, widespread use of Cu in all electrical devices will not be stopped, but the health of people directly related to its extraction, production, or distribution can be controlled, and the inhabitants of nearby towns can be protected. It is extremely difficult to assess the effects of copper on the human body because of its ubiquity and the increasing reports in the literature about its effects, including copper nanoparticles.

Effect of Dimethyloxalylglycine on Stem Cells Osteogenic Differentiation and Bone Tissue Regeneration-A Systematic Review

Dimethyloxalylglycine (DMOG) has been found to stimulate osteogenesis and angiogenesis of stem cells, promoting neo-angiogenesis in bone tissue regeneration. In this review, we conducted a comprehensive search of the literature to investigate the effects of DMOG on osteogenesis and bone regeneration. We screened the studies based on specific inclusion criteria and extracted relevant information from both in vitro and in vivo experiments. The risk of bias in animal studies was evaluated using the SYRCLE tool. Out of the 174 studies retrieved, 34 studies met the inclusion criteria (34 studies were analyzed in vitro and 20 studies were analyzed in vivo). The findings of the included studies revealed that DMOG stimulated stem cells' differentiation toward osteogenic, angiogenic, and chondrogenic lineages, leading to vascularized bone and cartilage regeneration. Addtionally, DMOG demonstrated therapeutic effects on bone loss caused by bone-related diseases. However, the culture environment in vitro is notably distinct from that in vivo, and the animal models used in vivo experiments differ significantly from humans. In summary, DMOG has the ability to enhance the osteogenic and angiogenic differentiation potential of stem cells, thereby improving bone regeneration in cases of bone defects. This highlights DMOG as a potential focus for research in the field of bone tissue regeneration engineering.

Associations of blood trace elements with bone mineral density: a population-based study in US adults

BACKGROUND

This study aimed to investigate the association between blood trace elements and bone mineral density (BMD) and to determine the association between blood trace elements and the risk of low BMD/osteoporosis among US adults.

METHODS

We performed a cross-sectional study using data from National Health and Nutrition Examination Survey (NHANES, 2011-2016). Multivariable linear regression models were employed to assess the associations of BMD in lumbar spine (LS-BMD), pelvic (PV-BMD) and total femur (TF-BMD) with blood trace elements, including Fe, Zn, Cu, Se, Mn, Cd, Pb, Hg. Additionally, the associations of low BMD/osteoporosis with blood trace elements were also evaluated using multivariable logistic regression.

RESULTS

Higher blood Pb levels were found associated with decreased LS-BMD (p for trend < 0.001), PV-BMD (p for trend = 0.007), and TF-BMD (p for trend = 0.003) in female, while higher blood Se levels were associated with increased PV-BMD in female (p for trend = 0.042); no linear association between BMD and other blood trace element was observed. Also, significant associations were found between Pb levels and the prevalence of low BMD (p for trend = 0.030) and the prevalence of osteoporosis (p for trend = 0.036), while association between other blood trace elements and low BMD/osteoporosis was not observed.

CONCLUSION

This study provides comprehensive insight into the association between blood trace elements and BMD and supports a detrimental effect of blood Pb levels on bone mass in women. Considering our analysis from a representative US general population, further study is warranted for the extreme levels of blood trace elements on bone metabolism.

HIF-1α and periodontitis: Novel insights linking host-environment interplay to periodontal phenotypes

Periodontitis, the sixth most prevalent epidemic disease globally, profoundly impacts oral aesthetics and masticatory functionality. Hypoxia-inducible factor-1α (HIF-1α), an oxygen-dependent transcriptional activator, has emerged as a pivotal regulator in periodontal tissue and alveolar bone metabolism, exerts critical functions in angiogenesis, erythropoiesis, energy metabolism, and cell fate determination. Numerous essential phenotypes regulated by HIF are intricately associated with bone metabolism in periodontal tissues. Extensive investigations have highlighted the central role of HIF and its downstream target genes and pathways in the coupling of angiogenesis and osteogenesis. Within this concise perspective, we comprehensively review the cellular phenotypic alterations and microenvironmental dynamics linking HIF to periodontitis. We analyze current research on the HIF pathway, elucidating its impact on bone repair and regeneration, while unraveling the involved cellular and molecular mechanisms. Furthermore, we briefly discuss the potential application of targeted interventions aimed at HIF in the field of bone tissue regeneration engineering. This review expands our biological understanding of the intricate relationship between the HIF gene and bone angiogenesis in periodontitis and offers valuable insights for the development of innovative therapies to expedite bone repair and regeneration.

Interaction between Mesenchymal Stem Cells and Immune Cells during Bone Injury Repair

Fractures are the most common large organ trauma in humans. The initial inflammatory response promotes bone healing during the initial post-fracture phase, but chronic and persistent inflammation due to infection or other factors does not contribute to the healing process. The precise mechanisms by which immune cells and their cytokines are regulated in bone healing remain unclear. The use of mesenchymal stem cells (MSCs) for cellular therapy of bone injuries is a novel clinical treatment approach. Bone progenitor MSCs not only differentiate into bone, but also interact with the immune system to promote the healing process. We review in vitro and in vivo studies on the role of the immune system and bone marrow MSCs in bone healing and their interactions. A deeper understanding of this paradigm may provide clues to potential therapeutic targets in the healing process, thereby improving the reliability and safety of clinical applications of MSCs to promote bone healing.

HIF-1α increases the osteogenic capacity of ADSCs by coupling angiogenesis and osteogenesis via the HIF-1α/VEGF/AKT/mTOR signaling pathway

BACKGROUND

Stabilization and increased activity of hypoxia-inducible factor 1-α (HIF-1α) can directly increase cancellous bone formation and play an essential role in bone modeling and remodeling. However, whether an increased HIF-1α expression in adipose-derived stem cells (ADSCs) increases osteogenic capacity and promotes bone regeneration is not known.

RESULTS

In this study, ADSCs transfected with small interfering RNA and HIF-1α overexpression plasmid were established to investigate the proliferation, migration, adhesion, and osteogenic capacity of ADSCs and the angiogenic ability of human umbilical vein endothelial cells (HUVECs). Overexpression of HIF-1α could promote the biological functions of ADSCs, and the angiogenic ability of HUVECs. Western blotting showed that the protein levels of osteogenesis-related factors were increased when HIF-1α was overexpressed. Furthermore, the influence of upregulation of HIF-1α in ADSC sheets on osseointegration was evaluated using a Sprague-Dawley (SD) rats implant model, in which the bone mass and osteoid mineralization speed were evaluated by radiological and histological analysis. The overexpression of HIF-1α in ADSCs enhanced bone remodeling and osseointegration around titanium implants. However, transfecting the small interfering RNA (siRNA) of HIF-1α in ADSCs attenuated their osteogenic and angiogenic capacity. Finally, it was confirmed in vitro that HIF-1α promotes osteogenic differentiation and the biological functions in ADSCs via the VEGF/AKT/mTOR pathway.

CONCLUSIONS

This study demonstrates that HIF-1α has a critical ability to promote osteogenic differentiation in ADSCs by coupling osteogenesis and angiogenesis via the VEGF/AKT/mTOR signaling pathway, which in turn increases osteointegration and bone formation around titanium implants.

Cuproptosis-a potential target for the treatment of osteoporosis

Osteoporosis is an age-related disease of bone metabolism marked by reduced bone mineral density and impaired bone strength. The disease causes the bones to weaken and break more easily. Osteoclasts participate in bone resorption more than osteoblasts participate in bone formation, disrupting bone homeostasis and leading to osteoporosis. Currently, drug therapy for osteoporosis includes calcium supplements, vitamin D, parathyroid hormone, estrogen, calcitonin, bisphosphates, and other medications. These medications are effective in treating osteoporosis but have side effects. Copper is a necessary trace element in the human body, and studies have shown that it links to the development of osteoporosis. Cuproptosis is a recently proposed new type of cell death. Copper-induced cell death regulates by lipoylated components mediated via mitochondrial ferredoxin 1; that is, copper binds directly to the lipoylated components of the tricarboxylic acid cycle, resulting in lipoylated protein accumulation and subsequent loss of iron-sulfur cluster proteins, leading to proteotoxic stress and eventually cell death. Therapeutic options for tumor disorders include targeting the intracellular toxicity of copper and cuproptosis. The hypoxic environment in bone and the metabolic pathway of glycolysis to provide energy in cells can inhibit cuproptosis, which may promote the survival and proliferation of various cells, including osteoblasts, osteoclasts, effector T cells, and macrophages, thereby mediating the osteoporosis process. As a result, our group tried to explain the relationship between the role of cuproptosis and its essential regulatory genes, as well as the pathological mechanism of osteoporosis and its effects on various cells. This study intends to investigate a new treatment approach for the clinical treatment of osteoporosis that is beneficial to the treatment of osteoporosis.

Insight into the effect of biomaterials on osteogenic differentiation of mesenchymal stem cells: A review from a mitochondrial perspective

Bone damage may be triggered by a variety of factors, and the damaged area often requires a bone graft. Bone tissue engineering can serve as an alternative strategy for repairing large bone defects. Mesenchymal stem cells (MSCs), the progenitor cells of connective tissue, have become an important tool for tissue engineering due to their ability to differentiate into a variety of cell types. The precise regulation of the growth and differentiation of the stem cells used for bone regeneration significantly affects the efficiency of this type of tissue engineering. During the process of osteogenic induction, the dynamics and function of localized mitochondria are altered. These changes may also alter the microenvironment of the therapeutic stem cells and result in mitochondria transfer. Mitochondrial regulation not only affects the induction/rate of differentiation, but also influences its direction, determining the final identity of the differentiated cell. To date, bone tissue engineering research has mainly focused on the influence of biomaterials on phenotype and nuclear genotype, with few studies investigating the role of mitochondria. In this review, we provide a comprehensive summary of researches into the role of mitochondria in MSCs differentiation and critical analysis regarding smart biomaterials that are able to "programme" mitochondria modulation was proposed. STATEMENT OF SIGNIFICANCE: : • This review proposed the precise regulation of the growth and differentiation of the stem cells used to seed bone regeneration. • This review addressed the dynamics and function of localized mitochondria during the process of osteogenic induction and the effect of mitochondria on the microenvironment of stem cells. • This review summarized biomaterials which affect the induction/rate of differentiation, but also influences its direction, determining the final identity of the differentiated cell through the regulation of mitochondria.

Dimethyloxalylglycine Attenuates Steroid-Associated Endothelial Progenitor Cell Impairment and Osteonecrosis of the Femoral Head by Regulating the HIF-1α Signaling Pathway

Endothelial impairment and dysfunction are closely related to the pathogenesis of steroid-associated osteonecrosis of the femoral head (SONFH). Recent studies have showed that hypoxia inducible factor-1α (HIF-1α) plays a crucial role in endothelial homeostasis maintenance. Dimethyloxalylglycine (DMOG) could suppress HIF-1 degradation and result in nucleus stabilization by repressing prolyl hydroxylase domain (PHD) enzymatic activity. Our results showed that methylprednisolone (MPS) remarkably undermined biological function of endothelial progenitor cells (EPC) by inhibiting colony formation, migration, angiogenesis, and stimulating senescence of EPCs, while DMOG treatment alleviated these effects by promoting HIF-1α signaling pathway, as evidenced by senescence-associated β-galactosidase (SA-β-Gal) staining, colony-forming unit, matrigel tube formation, and transwell assays. The levels of proteins related to angiogenesis were determined by ELISA and Western blotting. In addition, active HIF-1α bolstered the targeting and homing of endogenous EPCs to the injured endothelium in the femoral head. Histopathologically, our in vivo study showed that DMOG not only alleviated glucocorticoid-induced osteonecrosis but also promoted angiogenesis and osteogenesis in the femoral head as detected by microcomputed tomography (Micro-CT) analysis and histological staining of OCN, TRAP, and Factor Ⅷ. However, all of these effects were impaired by an HIF-1α inhibitor. These findings demonstrate that targeting HIF-1α in EPCs may constitute a novel therapeutic approach for the treatment of SONFH.

Iron, Zinc, Copper, Cadmium, Mercury, and Bone Tissue

The paper presents the current understanding on the effects of five metals on bone tissue, namely iron, zinc, copper, cadmium, and mercury. Iron, zinc, and copper contribute significantly to human and animal metabolism when present in sufficient amounts, but their excess or shortage increases the risk of developing bone disorders. In contrast, cadmium and mercury serve no physiological purpose and their long-term accumulation damages the osteoarticular system. We discuss the methods of action and interactions between the discussed elements as well as the concentrations of each element in distinct bone structures.

HIF-1α Regulates Bone Homeostasis and Angiogenesis, Participating in the Occurrence of Bone Metabolic Diseases

In the physiological condition, the skeletal system's bone resorption and formation are in dynamic balance, called bone homeostasis. However, bone homeostasis is destroyed under pathological conditions, leading to the occurrence of bone metabolism diseases. The expression of hypoxia-inducible factor-1α (HIF-1α) is regulated by oxygen concentration. It affects energy metabolism, which plays a vital role in preventing bone metabolic diseases. This review focuses on the HIF-1α pathway and describes in detail the possible mechanism of its involvement in the regulation of bone homeostasis and angiogenesis, as well as the current experimental studies on the use of HIF-1α in the prevention of bone metabolic diseases. HIF-1α/RANKL/Notch1 pathway bidirectionally regulates the differentiation of macrophages into osteoclasts under different conditions. In addition, HIF-1α is also regulated by many factors, including hypoxia, cofactor activity, non-coding RNA, trace elements, etc. As a pivotal pathway for coupling angiogenesis and osteogenesis, HIF-1α has been widely studied in bone metabolic diseases such as bone defect, osteoporosis, osteonecrosis of the femoral head, fracture, and nonunion. The wide application of biomaterials in bone metabolism also provides a reasonable basis for the experimental study of HIF-1α in preventing bone metabolic diseases.

Dimethyloxalylglycine (DMOG), a Hypoxia Mimetic Agent, Does Not Replicate a Rat Pheochromocytoma (PC12) Cell Biological Response to Reduced Oxygen Culture

Cells respond to reduced oxygen availability predominately by activation of the hypoxia-inducible factor (HIF) pathway. HIF activation upregulates hundreds of genes that help cells survive in the reduced oxygen environment. The aim of this study is to determine whether chemical-induced HIF accumulation mimics all aspects of the hypoxic response of cells. We compared the effects of dimethyloxalylglycine (DMOG) (a HIF stabiliser) on PC12 cells cultured in air oxygen (20.9% O_2, AO) with those cultured in either intermittent 20.9% O₂ to 2% O₂ (IH) or constant 2% O₂ (CN). Cell viability, cell cycle, HIF accumulation, reactive oxygen species (ROS) formation, mitochondrial function and differentiation were used to characterise the PC12 cells and evaluate the impact of DMOG. IH and CN culture reduced the increase in cell numbers after 72 and 96 h and MTT activity after 48 h compared to AO culture. Further, DMOG supplementation in AO induced a dose-dependent reduction in the increase in PC12 cell numbers and MTT activity. IH-cultured PC12 cells displayed increased and sustained HIF-1 expression over 96 h. This was accompanied by increased ROS and mitochondrial burden. PC12 cells in CN displayed little changes in HIF-1 expression or ROS levels. DMOG (0.1 mM) supplementation resulted in an IH-like HIF-1 profile. The mitochondrial burden and action potential of DMOG-supplemented PC12 cells did not mirror those seen in other conditions. DMOG significantly increased S phase cell populations after 72 and 96 h. No significant effect on PC12 cell differentiation was noted with IH and CN culture without induction by nerve growth factor (NGF), while DMOG significantly increased PC12 cell differentiation with and without NGF. In conclusion, DMOG and reduced oxygen levels stabilise HIF and affect mitochondrial activity and cell behaviour. However, DMOG does not provide an accurate replication of the reduced oxygen environments.

Vascularized Tumor Spheroid-on-a-Chip Model Verifies Synergistic Vasoprotective and Chemotherapeutic Effects

Prolyl hydroxylases (PHD) inhibitors have been observed to improve drug distribution in mice tumors via blood vessel normalization, increasing the effectiveness of chemotherapy. These effects are yet to be demonstrated in human cell models. Tumor spheroids are three-dimensional cell clusters that have demonstrated great potential in drug evaluation for personalized medicine. Here, we used a perfusable vascularized tumor spheroid-on-a-chip to simulate the tumor microenvironment in vivo and demonstrated that the PHD inhibitor dimethylallyl glycine prevents the degradation of normal blood vessels while enhancing the efficacy of the anticancer drugs paclitaxel and cisplatin in human esophageal carcinoma (Eca-109) spheroids. Our results point to the potential of this model to evaluate anticancer drugs under more physiologically relevant conditions.

Osteostatin improves the Osteogenic differentiation of mesenchymal stem cells and enhances angiogenesis through HIF-1α under hypoxia conditions in vitro

BACKGROUND

Hypoxia conditions induced by bone defects would prolong the duration of bone regeneration. The effect of osteostatin (OST) on the osteogenic differentiation of mesenchymal stem cells (MSCs) and angiogenesis under hypoxia conditions remain unexplored.

METHODS

SPF mice were obtained, and MSCs were isolated from bone marrow. MSCs were treated with 1% oxygen for hypoxia induction, and 200 nM of OST was used to treat cells under nomorxia or hypoxia conditions. Cell proliferation was evaluated using CCK8 assay, and trypan blue staining was implemented for determining cell death ratio. Alkaline phosphatase activity and alizarin redS staining was conducted to histologically evaluated osteogenic differentiation. Flow cytometry was used for the detection of CD31^hiEmcn^hi cells (Type H ECs), whose migration was detected by Transwell assay and angiogenesis was measured by tube formation assay. Protein level was measured by western blotting and mRNA level was monitored via RT-qPCR.

RESULTS

The MSC proliferation was enhanced by OST under hypoxia conditions. The osteogenic differentiation of MSCs was decreased under hypoxia conditions, and treatment of OST significantly reversed its inhibitory effect. The hypoxia treated culture medium of MSCs promoted the proliferation, migration, and angiogenesis of type H ECs, while the effects were further strengthened by OST addition. HIF-1α was found to be upregulated in hypoxia treated MSCs, whereas silencing of HIF-1α had reversed effects on the angiogenic capacity of Type H ECs.

CONCLUSION

OST improved the proliferation and osteogenic differentiation of MSCs and further promoted angiogenesis of type H ECs through upregulating HIF-1α expression.

Dimethyloxaloylglycine promotes spermatogenesis activity of spermatogonial stem cells in Bama minipigs

Background

The testis has been reported to be a naturally O₂-deprived organ, dimethyloxaloylglycine (DMOG) can inhibit hypoxia inducible factor-1alpha (HIF-1α) subject to degradation under normal oxygen condition in cells.

Objectives

The objective of this study is to detect the effects of DMOG on the proliferation and differentiation of spermatogonial stem cells (SSCs) in Bama minipigs.

Methods

Gradient concentrations of DMOG were added into the culture medium, HIF-1α protein in SSCs was detected by western blot analysis, the relative transcription levels of the SSC-specific genes were analyzed using quantitative reverse transcription polymerase chain reaction (qRT-PCR). Six days post-induction, the genes related to spermatogenesis were detected by qRT-PCR, and the DNA content was determined by flow cytometry.

Results

Results revealed that the levels of HIF-1α protein increased in SSCs with the DMOG treatment in a dose-dependent manner. The relative transcription levels of SSC-specific genes were significantly upregulated (p < 0.05) by activating HIF-1α expression. The induction results showed that DMOG significantly increased (p < 0.05) the spermatogenesis capability of SSCs, and the populations of haploid cells significantly increased (p < 0.05) in DMOG-treated SSCs when compared to those in DMOG-untreated SSCs.

Conclusion

We demonstrate that DMOG can promote the spermatogenesis activity of SSCs.

Chemically induced hypoxia by dimethyloxalylglycine (DMOG)-loaded nanoporous silica nanoparticles supports endothelial tube formation by sustained VEGF release from adipose tissue-derived stem cells

Inadequate vascularization leading to insufficient oxygen and nutrient supply in deeper layers of bioartificial tissues remains a limitation in current tissue engineering approaches to which pre-vascularization offers a promising solution. Hypoxia triggering pre-vascularization by enhanced vascular endothelial growth factor (VEGF) expression can be induced chemically by dimethyloxalylglycine (DMOG). Nanoporous silica nanoparticles (NPSNPs, or mesoporous silica nanoparticles, MSNs) enable sustained delivery of molecules and potentially release DMOG allowing a durable capillarization of a construct. Here we evaluated the effects of soluble DMOG and DMOG-loaded NPSNPs on VEGF secretion of adipose tissue-derived stem cells (ASC) and on tube formation by human umbilical vein endothelial cells (HUVEC)-ASC co-cultures. Repeated doses of 100 µM and 500 µM soluble DMOG on ASC resulted in 3- to 7-fold increased VEGF levels on day 9 (P < 0.0001). Same doses of DMOG-NPSNPs enhanced VEGF secretion 7.7-fold (P < 0.0001) which could be maintained until day 12 with 500 µM DMOG-NPSNPs. In fibrin-based tube formation assays, 100 µM DMOG-NPSNPs had inhibitory effects whereas 50 µM significantly increased tube length, area and number of junctions transiently for 4 days. Thus, DMOG-NPSNPs supported endothelial tube formation by upregulated VEGF secretion from ASC and thus display a promising tool for pre-vascularization of tissue-engineered constructs. Further studies will evaluate their effect in hydrogels under perfusion.

Lithium chloride prevents glucocorticoid-induced osteonecrosis of femoral heads and strengthens mesenchymal stem cell activity in rats

Background:

Accumulating evidence suggests that lithium influences mesenchymal stem cell (MSC) proliferation and osteogenic differentiation. As decreased bone formation in femoral heads is induced by glucocorticoids (GCs), we hypothesized that lithium has a protective effect on GC-induced osteonecrosis of femoral heads (ONFH).

Methods:

A rat ONFH model was induced by methylprednisolone (MP) and the effect of lithium chloride on the models was evaluated. Micro-computed tomography (CT)-based angiography and bone scanning were performed to analyze the vessels and bone structure in the femoral heads. Hematoxylin and eosin and immunohistochemical staining were performed to evaluate the trabecular structure and osteocalcin (OCN) expression, respectively. Bone marrow-derived MSCs were isolated from the models, and their proliferative and osteogenic ability was evaluated. Western blotting and quantitative real-time polymerase chain reaction were performed to detect osteogenic-related proteins including Runx2, alkaline phosphatase, and Collagen I.

Results:

Micro-CT analysis showed a high degree of osteonecrotic changes in the rats that received only MP injection. Treatment with lithium reduced this significantly in rats that received lithium (MP + Li group); while 18/20 of the femoral heads in the MP showed severe osteonecrosis, only 5/20 in the MP + Li showed mild osteonecrotic changes. The MP + Li group also displayed a higher vessel volume than the MP group (0.2193 mm³vs. 0.0811 mm³, P < 0.05), shown by micro-CT-based angiography. Furthermore, histological analysis showed better trabecular structures and more OCN expression in the femoral heads of the MP + Li group compared with the MP group. The ex vivo investigation indicated higher proliferative and osteogenic ability and upregulated osteogenic-related proteins in MSCs extracted from rats in the MP + Li group than that in the MP group.

Conclusions:

We concluded that lithium chloride has a significant protective effect on GC-induced ONFH in rats and that lithium also enhances MSC proliferation and osteogenic differentiation in rats after GC administration.

Copper as Dietary Supplement for Bone Metabolism: A Review

While in vitro and animal studies of osteoblastic and osteoclastic activity as well as bone resistance for copper are numerous, and the results encouraging in terms of regulation, human studies are scarce. The aim of this narrative review was to investigate the correlation of blood copper, daily copper intake, and copper supplementation with bone mineral density. This review included 10 eligible studies: five studies concerned copper blood levels, one study concerned daily copper intake, and four studies concerned copper supplementation. Blood copper levels did not show statistically significant differences in four of the studies analyzed, while only one study showed differences between osteoporotic and healthy women, although only with women between 45 and 59 years of age and not between 60 and 80 years of age. The dietary copper intake among women with or without osteoporosis did not show any differences. Only one study with a small sample of subjects carried out these assessments; therefore, it is a topic that the literature must deepen with further studies. The two studies that analyzed the integration of copper (2.5-3 mg/day) only showed good results in terms of slowing down bone mineral loss and reducing resorption markers, confirming the effectiveness of copper supplementation on bone metabolism.

Dimethyloxalylglycine, a small molecule, synergistically increases the homing and angiogenic properties of human mesenchymal stromal cells when cultured as 3D spheroids

Strategies aiming at increasing the survival and paracrine activity of human mesenchymal stromal cells (MSCs) are of utmost importance to achieve the full therapeutic potential of these cells. Herein, we propose both physical and biochemical strategies to enhance the survival, homing, angiogenic, and immunomodulatory properties of MSCs in vitro. To that purpose, we compared the effect of exposing either 2D monolayer or 3D spheroids of MSCs to (i) hypoxia (2% O₂ ) or to (ii) a hypoxic-mimetic small molecule, dimethyloxalylglycine (DMOG), with cells cultured at 21% O₂ . 3D-cultured MSC spheroids evidenced higher survival upon exposure to oxidative stress and expressed higher levels of factors involved in tissue repair processes, namely tumor necrosis factor-stimulated gene-6, matrix metalloproteinase-2, and vascular endothelial growth factor. MSCs cultured as 3D spheroids and further exposed to hypoxia or hypoxic-mimetic conditions provided by DMOG synergistically favored the expression of the cell surface marker C-X-C chemokine receptor type-4, involved in homing processes to injured tissues, and adhesion to extracellular matrix components as fibronectin. These results highlight the role of ex vivo preconditioning approaches, presenting a novel strategy that combine biochemical stimuli with 3D spheroid organization of MSCs to maximize their tissue regeneration potential.

Dimethyloxallyl glycine/nanosilicates-loaded osteogenic/angiogenic difunctional fibrous structure for functional periodontal tissue regeneration

The coupled process of osteogenesis-angiogenesis plays a crucial role in periodontal tissue regeneration. Although various cytokines or chemokines have been widely applied in periodontal in situ tissue engineering, most of them are macromolecular proteins with the drawbacks of short effective half-life, poor stability and high cost, which constrain their clinical translation. Our study aimed to develop a difunctional structure for periodontal tissue regeneration by incorporating an angiogenic small molecule, dimethyloxalylglycine (DMOG), and an osteoinductive inorganic nanomaterial, nanosilicate (nSi) into poly (lactic-co-glycolic acid) (PLGA) fibers by electrospinning. The physiochemical properties of DMOG/nSi-PLGA fibrous membranes were characterized. Thereafter, the effect of DMOG/nSi-PLGA membranes on periodontal tissue regeneration was evaluated by detecting osteogenic and angiogenic differentiation potential of periodontal ligament stem cells (PDLSCs) in vitro. Additionally, the fibrous membranes were transplanted into rat periodontal defects, and tissue regeneration was assessed with histological evaluation, micro-computed tomography (micro-CT), and immunohistochemical analysis. DMOG/nSi-PLGA membranes possessed preferable mechanical property and biocompatibility. PDLSCs seeded on the DMOG/nSi-PLGA membranes showed up-regulated expression of osteogenic and angiogenic markers, higher alkaline phosphatase (ALP) activity, and more tube formation in comparison with single application. Further, in vivo study showed that the DMOG/nSi-PLGA membranes promoted recruitment of CD90+/CD34− stromal cells, induced angiogenesis and osteogenesis, and regenerated cementum-ligament-bone complex in periodontal defects. Consequently, the combination of DMOG and nSi exerted admirable effects on periodontal tissue regeneration. DMOG/nSi-PLGA fibrous membranes could enhance and orchestrate osteogenesis-angiogenesis, and may have the potential to be translated as an effective scaffold in periodontal tissue engineering.

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Dual-load fibrous structure possessed preferable mechanical property and biocompatibility.

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Fibrous structure can orchestrate and enhance osteogenesis-angiogenesis coupling.

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Difunctional fibrous structure can recruit CD90+/CD34− stromal cells to periodontal defects.

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Difunctional fibrous structure obtained functional periodontal tissue regeneration.

Delivery of dimethyloxalylglycine in calcined bone calcium scaffold to improve osteogenic differentiation and bone repair

As hypoxia plays a vital role in the angiogenic-osteogenic coupling, using proline hydroxylase inhibitors to manipulate hypoxia-inducible factors has become a strategy to improve the osteogenic properties of biomaterials. Dimethyloxallyl glycine (DMOG) is a 2-ketoglutarate analog, a small molecular compound that competes for 2-ketoglutaric acid to inhibit proline hydroxylase. In order to improve the osteogenic ability of calcined bone calcium (CBC), a new hypoxia-mimicking scaffold (DMOG/Collagen/CBC) was prepared by immersing it in the DMOG-Collagen solution, followed by freeze-drying. All coated CBC scaffolds retained the inherent natural porous architecture and showed excellent biocompatibility. A slow release of DMOG by the DMOG-loaded CBC scaffolds for up to one week was observed in in vitro experiments. Moreover, the DMOG/Collagen/CBC composite scaffold was found to significantly stimulate bone marrow stromal cells to express osteogenic and angiogenic genes in vitro. In addition, the osteogenic properties of three kinds of scaffolds, raw CBC, Collagen/CBC, and DMOG/Collagen/CBC, were evaluated by histology using the rabbit femoral condyle defect model. Histomorphometric analyses showed that the newly formed bone (BV/TV) in the DMOG/Collagen/CBC group was significantly higher than that of the Collagen/CBC group. However, immunostaining of CD31 and Runx2 expression between these two groups showed no significant difference at this time point. Our results indicate that DMOG-coated CBC can promote osteogenic differentiation and bone healing, and show potential for clinical application in bone tissue engineering.

Proangiogenic Hypoxia-Mimicking Agents Attenuate Osteogenic Potential of Adipose Stem/Stromal Cells

BACKGROUND

Insufficient vascularization hampers bone tissue engineering strategies for reconstructing large bone defects. Delivery of prolyl-hydroxylase inhibitors (PHIs) is an interesting approach to upregulate vascular endothelial growth factor (VEGF) by mimicking hypoxic stabilization of hypoxia-inducible factor-1alpha (HIF-1α). This study assessed two PHIs: dimethyloxalylglycine (DMOG) and baicalein for their effects on human adipose tissue-derived mesenchymal stem/stromal cells (AT-MSCs).

METHODS

Isolated AT-MSCs were characterized and treated with PHIs to assess the cellular proliferation response. Immunostaining and western-blots served to verify the HIF-1α stabilization response. The optimized concentrations for long-term treatment were tested for their effects on the cell cycle, apoptosis, cytokine secretion, and osteogenic differentiation of AT-MSCs. Gene expression levels were evaluated for alkaline phosphatase (ALPL), bone morphogenetic protein 2 (BMP2), runt-related transcription factor 2 (RUNX2), vascular endothelial growth factor A (VEGFA), secreted phosphoprotein 1 (SPP1), and collagen type I alpha 1 (COL1A1). In addition, stemness-related genes Kruppel-like factor 4 (KLF4), Nanog homeobox (NANOG), and octamer-binding transcription factor 4 (OCT4) were assessed.

RESULTS

PHIs stabilized HIF-1α in a dose-dependent manner and showed evident dose- and time dependent antiproliferative effects. With doses maintaining proliferation, DMOG and baicalein diminished the effect of osteogenic induction on the expression of RUNX2, ALPL, and COL1A1, and suppressed the formation of mineralized matrix. Suppressed osteogenic response of AT-MSCs was accompanied by an upregulation of stemness-related genes.

CONCLUSION

PHIs significantly reduced the osteogenic differentiation of AT-MSCs and rather upregulated stemness-related genes. PHIs proangiogenic potential should be weighed against their longterm direct inhibitory effects on the osteogenic differentiation of AT-MSCs.

Adjuvant drug-assisted bone healing: Part II - Modulation of angiogenesis

 The treatment of critical-size bone defects following complicated fractures, infections or tumor resections is a major challenge. The same applies to fractures in patients with impaired bone healing due to systemic inflammatory and metabolic diseases. Despite considerable progress in development and establishment of new surgical techniques, design of bone graft substitutes and imaging techniques, these scenarios still represent unresolved clinical problems. However, the development of new active substances offers novel potential solutions for these issues. This work discusses therapeutic approaches that influence angiogenesis or hypoxic situations in healing bone and surrounding tissue. In particular, literature on sphingosine-1-phosphate receptor modulators and nitric oxide (NO•) donors, including bi-functional (hybrid) compounds like NO•-releasing cyclooxygenase-2 inhibitors, was critically reviewed with regard to their local and systemic mode of action.

Dimethyloxaloylglycine-stimulated human bone marrow mesenchymal stem cell-derived exosomes enhance bone regeneration through angiogenesis by targeting the AKT/mTOR pathway

Background

Mesenchymal stem cell (MSC)-derived exosomes have been recognized as new candidate agents for treating critical-sized bone defects; they promote angiogenesis and may be an alternative to cell therapy. In this study, we evaluated whether exosomes derived from bone marrow-derived MSCs (BMSCs) preconditioned with a low dose of dimethyloxaloylglycine (DMOG), DMOG-MSC-Exos, exert superior proangiogenic activity in bone regeneration and the underlying mechanisms involved.

Methods

To investigate the effects of these exosomes, scratch wound healing, cell proliferation, and tube formation assays were performed in human umbilical vein endothelial cells (HUVECs). To test the effects in vivo, a critical-sized calvarial defect rat model was established. Eight weeks after the procedure, histological/histomorphometrical analysis was performed to measure bone regeneration, and micro-computerized tomography was used to measure bone regeneration and neovascularization.

Results

DMOG-MSC-Exos activated the AKT/mTOR pathway to stimulate angiogenesis in HUVECs. This contributed to bone regeneration and angiogenesis in the critical-sized calvarial defect rat model in vivo.

Conclusions

Low doses of DMOG trigger exosomes to exert enhanced proangiogenic activity in cell-free therapeutic applications.

Review of the Pathways Involved in the Osteogenic Differentiation of Adipose-Derived Stem Cells

Grafts and prosthetic materials used for the repair of bone defects are often accompanied by comorbidity and rejection. Therefore, there is an immense need for novel approaches to combating the issues surrounding such defects. Because of their accessibility, substantial proportion, and osteogenic differentiation potential, adipose-derived stem cells (ASCs) make for an ideal source of bone tissue in regenerative medicine. However, efficient induction of ASCs toward an osteoblastic lineage in vivo is met with challenges, and many signaling pathways must come together to secure osteoblastogenesis. Among them are bone morphogenic protein, wingless-related integration site protein, Notch, Hedgehog, fibroblast growth factor, vascular endothelial growth factor, and extracellular regulated-signal kinase. The goal of this literature review is to conglomerate the present research on these pathways to formulate a better understanding of how ASCs are most effectively transformed into bone in the context of tissue engineering.

Hypoxia-Mimicking Cobalt-Doped Borosilicate Bioactive Glass Scaffolds with Enhanced Angiogenic and Osteogenic Capacity for Bone Regeneration

The osteogenic capacity of synthetic bone substitutes is will be highly stimulated by a well-established functional vascularized network. Cobalt (Co) ions are known that can generate a hypoxia-like response and stimulates the production of kinds of angiogenic factors. Herein, we investigated the mechanism of cobalt-doped bioactive borosilicate (36B2O3, 22CaO, 18SiO2, 8MgO, 8K2O, 6Na2O, 2P2O5; mol%) glass scaffolds for bone tissues repairing and blood vessel formation in the critical-sized cranial defect site of rats and their effects on the hBMSCs in vitro were researched. The scaffolds can control release Co2+ ions and convert into hydroxyapatite soaking in simulative body fluids (SBF). The fabircated scaffolds without cytotoxic strongly improves HIF-1α generation, VEGF protein secretion, ALP activity and upregulates the expression of osteoblast and angiogenic relative genes in hBMSCs. Eight weeks after implantation, the bioactive glass scaffolds with 3wt % CoO remarkablely enhance bone regeneration and blood vascularized network at the defective site. In conclusion, as a graft material for bone defects, low-oxygen simulated cobalt-doped bioactive glass scaffold is promising.

Impaired Bone Regenerative Effect of Exosomes Derived from Bone Marrow Mesenchymal Stem Cells in Type 1 Diabetes

Stem cell‐derived exosomes have exhibited promise for applications in tissue regeneration. However, one major problem for stem cell‐derived exosome therapies is identifying appropriate source cells. In the present study, we aimed to compare the bone regenerative effect of exosomes secreted by bone marrow mesenchymal stem cells (BMSCs) derived from type 1 diabetes rats (dBMSC‐exos) and exosomes secreted by BMSCs derived from normal rats (nBMSC‐exos). BMSCs were isolated from rats with streptozotocin‐induced diabetes and normal rats. dBMSC‐exos and nBMSC‐exos were isolated by an ultracentrifugation method and identified. The effects of dBMSC‐exos and nBMSC‐exos on the proliferation and migration of BMSCs and human umbilical vein endothelial cells (HUVECs) were investigated. The effects of exosomes on the osteogenic differentiation of BMSCs and the angiogenic activity of HUVECs were compared. Finally, a rat calvarial defect model was used to compare the effects of exosomes on bone regeneration and neovascularization in vivo. In vitro, dBMSC‐exos and nBMSC‐exos both enhanced the osteogenic differentiation of BMSCs and promoted the angiogenic activity of HUVECs, but nBMSC‐exos had a greater effect than dBMSC‐exos. Similarly, in vivo, both dBMSC‐exos and nBMSC‐exos promoted bone regeneration and neovascularization in rat calvarial defects, but the therapeutic effect of nBMSC‐exos was superior to that of dBMSC‐exos. The present study demonstrates for the first time that the bone regenerative effect of exosomes derived from BMSCs is impaired in type 1 diabetes, indicating that for patients with type 1 diabetes, the autologous transplantation of BMSC‐exos to promote bone regeneration may be inappropriate. stem cells translational medicine2019;8:593–605

Catalpol promotes the osteogenic differentiation of bone marrow mesenchymal stem cells via the Wnt/β-catenin pathway

Background

Rehmanniae Radix is a traditional herbal medicine in East Asia that has been widely used to treat patients with osteoporosis. However, the effect of catalpol, the primary active principle component of Rehmanniae Radix, on the function of bone marrow mesenchymal stem cells (BMSCs) and the underlying molecular mechanisms associated with its activity remain poorly understood.

Methods

The effect of catalpol on the proliferation of BMSCs was evaluated using a Cell Counting Kit-8 assay. Alkaline phosphatase (ALP) staining, ALP activity and Alizarin Red staining were performed to elucidate the effect of catalpol on the osteogenesis of BMSCs. qRT-PCR, Western blotting and immunofluorescence were performed to evaluate the expression of osteo-specific markers and the Wnt/β-catenin signalling-related genes and proteins. Moreover, a rat critical-sized calvarial defect model and a rat ovariectomy model were used to assess the effect of catalpol on bone regeneration in vivo.

Results

Catalpol significantly enhanced osteoblast-specific gene expression, alkaline phosphatase activity and calcium deposition in BMSCs in vitro. This phenomenon was accompanied by an upregulation of Wnt/β-catenin signalling. In addition, the enhanced osteogenesis due to catalpol treatment was partially reversed by a Wnt/β-catenin antagonist. Furthermore, catalpol increased the bone healing capacity of BMSCs in a rat critical-sized calvarial defect model and attenuated bone loss in a rat ovariectomy model.

Conclusions

These data suggest that catalpol enhances the osteogenic differentiation of BMSCs, partly via activation of the Wnt/β-catenin pathway. Catalpol may provide a new strategy for bone tissue engineering and can be a potential agent for the treatment of postmenopausal osteoporosis.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1143-y) contains supplementary material, which is available to authorized users.

3D-porous β-tricalcium phosphate-alginate-gelatin scaffold with DMOG delivery promotes angiogenesis and bone formation in rat calvarial defects

Hypoxia-inducible factor-1α (HIF-1α), a well-studied angiogenesis pathway, plays an essential role in angiogenesis-osteogenesis coupling. Targeting the HIF-1a pathway frequently leads to successful reconstruction of large-sized bone defects through promotion of angiogenesis. Dimethyloxalylglycine (DMOG) small molecule regulates the stability of HIF-1α at normal oxygen tension by mimicking hypoxia, which subsequently accelerates angiogenesis. The current study aims to develop a novel construct by seeding adipose derived mesenchymal stem cells (ADMSCs) onto a scaffold that contains DMOG to induce angiogenesis and regeneration of a critical size calvarial defect in a rat model. The spongy scaffolds have been synthesized in the presence and absence of DMOG and analyzed in terms of morphology, porosity, pore size, mechanical properties and DMOG release profile. The effect of DMOG delivery on cellular behaviors of adhesion, viability, osteogenic differentiation, and angiogenesis were subsequently evaluated under in vitro conditions. Histological analysis of cell-scaffold constructs were also performed following transplantation into the calvarial defect. Physical characteristics of fabricated scaffolds confirmed higher mechanical strength and surface roughness of DMOG-loaded scaffolds. Scanning electron microscopy (SEM) images and MTT assay demonstrated the attachment and viability of ADMSCs in the presence of DMOG, respectively. Osteogenic activity of ADMSCs that included alkaline phosphatase (ALP) activity and calcium deposition significantly increased in the DMOG-loaded scaffold. Computed tomography (CT) imaging combined with histomorphometry and immunohistochemistry analysis showed enhanced bone formation and angiogenesis in the DMOG-loaded scaffolds. Therefore, spongy scaffolds that contained DMOG and had angiogenesis ability could be utilized to enhance bone regeneration of large-sized bone defects.

Silk Fibroin Microparticles with Hollow Mesoporous Silica Nanocarriers Encapsulation for Abdominal Wall Repair

Therapeutic vascularization appears to be an effective way of repairing abdominal wall defects. Attempts to implement this treatment tend to focus on the generation of featured drug carriers with the ability effectively to encapsulate the angiogenesis-stimulating agents and control their release to maintain an appropriate concentration at the injured area. Here, a new type of composite microparticle (CM) composed of silk fibroin (SF) and hollow mesoporous silica nanocarriers (HMSNs) is presented for therapeutic agent delivery. The CMs are generated by drying microfluidic emulsion templates of HMSN-dispersed SF solution. The resultant CMs have a distinctive micro-nanostructure, in which two barriers control the drug release. The encapsulated HMSNs increase the drug-carrying capacity of the CMs, and also form the first barrier via physical absorption. The microfluidic SF microparticles not only provide a shell with excellent monodispersity and biocompatibility but also form the second barrier via efficient encapsulation. Because of these superior properties of the CMs, the loaded drugs can be delivered with a satisfactory activity at the required rate, making them ideal for implementing therapeutic vascularization and repairing abdominal wall defects.

Injectable angiogenic and osteogenic carrageenan nanocomposite hydrogel for bone tissue engineering

Functional biomaterials that couple angiogenesis and osteogenesis processes are vital for bone tissue engineering and bone remodeling. Herein we developed an injectable carrageenan nanocomposite hydrogel incorporated with whitlockite nanoparticles and an angiogenic drug, dimethyloxallylglycine. Synthesized whitlockite nanoparticles and nanocomposite hydrogels were characterized using SEM, TEM, EDS and FTIR. Developed hydrogels were injectable, mechanically stable, cytocompatible and has better protein adsorption. Incorporation of dimethyloxallylglycine resulted in initial burst release followed by sustained release for 7 days. Human umbilical vein endothelial cells exposed to dimethyloxallylglycine incorporated nanocomposite hydrogel showed enhanced cell migration and capillary tube-like structure formation. Osteogenic differentiation in rat adipose derived mesenchymal stem cells after 7 and 14 days revealed increased levels of alkaline phosphatase activity in vitro. Furthermore, cells exposed to nanocomposite hydrogel revealed enhanced protein expressions of RUNX2, COL and OPN. Overall, these results suggest that incorporation of whitlockite and dimethyloxallylglycine in carrageenan hydrogel promoted osteogenesis and angiogenesis in vitro.

Safflower yellow promotes angiogenesis through p-VHL/ HIF-1α/VEGF signaling pathway in the process of osteogenic differentiation

OBJECTIVE

Safflower yellow (SY) is an active component ofCarthamus tinctorius L. that is widely used in orthopedics. This study aimed to evaluate the role of SY in angiogenesis and osteogenic differentiation.

METHODS

The migration and in vitro angiogenesis of SY (4.5, 9.0, 18 μg/ml)-treated human umbilical vein endothelial cells (HUVEC-12) were assessed by transwell and tube formation assay, respectively. Osteogenic differentiation ability was detected by alkaline phosphatase (ALP) and Alizarin Red S staining. The mRNA and protein expressions of related markers were determined by RT-qPCR and Western blot.

RESULTS

The migration and tube formation ability of HUVEC-12 were promoted by SY. Furthermore, SY facilitated the angiogenesis and osteogenic differentiation in the co-culture of HUVEC-12 and BMSCs by increasing hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), Angiopoietin-2 (Ang-2), ALP, runt-related transcription factor 2 (Runx2) and osteopontin-1 (OPN-1) levels. Inhibition of HIF-1α expression by 3-(5-hydroxymethl-2-furyl)-1-benzylindazole (YC-1), restrained SY-induced proliferation, migration and angiogenesis of HUVEC-12 and the increased protein levels of VEGF, Ang-2, ALP, Runx2 and OPN-1. Finally, WD repeat and SOCS box-containing protein-1 (WSB-1)/Von Hippel-Lindau protein (p-VHL) pathway was involved in the beneficial effect of SY.

CONCLUSION

SY promotes osteogenic differentiation via enhancing angiogenesis by regulating pVHL/HIF-1α/VEGF signaling pathway.

Chemical Activation of the Hypoxia-Inducible Factor Reversibly Reduces Tendon Stem Cell Proliferation, Inhibits Their Differentiation, and Maintains Cell Undifferentiation

Adult stem cell-based therapeutic approaches for tissue regeneration have been proposed for several years. However, adult stem cells are usually limited in number and difficult to be expanded in vitro, and they usually tend to quickly lose their potency with passages, as they differentiate and become senescent. Culturing stem cells under reduced oxygen tensions (below 21%) has been proposed as a tool to increase cell proliferation, but many studies reported opposite effects. In particular, cell response to hypoxia seems to be very stem cell type specific. Nonetheless, it is clear that a major role in this process is played by the hypoxia inducible factor (HIF), the master regulator of cell response to oxygen deprivation, which affects cell metabolism and differentiation. Herein, we report that a chemical activation of HIF in human tendon stem cells reduces their proliferation and inhibits their differentiation in a reversible and dose-dependent manner. These results support the notion that hypoxia, by activating HIF, plays a crucial role in preserving stem cells in an undifferentiated state in the “hypoxic niches” present in the tissue in which they reside before migrating in more oxygenated areas to heal a damaged tissue.

Composite biopolymers for bone regeneration enhancement in bony defects

For the past century, various biomaterials have been used in the treatment of bone defects and fractures. Their role as potential substitutes for human bone grafts increases as donors become scarce. Metals, ceramics and polymers are all materials that confer different advantages to bone scaffold development. For instance, biocompatibility is a highly desirable property for which naturally-derived polymers are renowned. While generally applied separately, the use of biomaterials, in particular natural polymers, is likely to change, as biomaterial research moves towards mixing different types of materials in order to maximize their individual strengths. This review focuses on osteoconductive biocomposite scaffolds which are constructed around natural polymers and their performance at the in vitro/in vivo stages and in clinical trials.

Dimethyloxaloylglycine increases bone repair capacity of adipose-derived stem cells in the treatment of osteonecrosis of the femoral head

Mesenchymal stem cells have been widely studied to promote local bone regeneration of osteonecrosis of the femoral head (ONFH). Previous studies observed that dimethyloxaloylglycine (DMOG) enhanced the angiogenic and osteogenic activity of mesenchymal stem cells by activating the expression of hypoxia inducible factor-1α (HIF-1α), thereby improving the bone repair capacity of mesenchymal stem cells. In the present study, it was investigated whether DMOG could increase the bone repair capacity of adipose-derived stem cells (ASCs) in the treatment of ONFH. Western blot analysis was performed to detect HIF-1α protein expression in ASCs treated with different concentrations of DMOG. The results showed DMOG enhanced HIF-1α expression in ASCs in a dose-dependent manner at least for 7 days. Furthermore, DMOG-treated ASCs were transplanted into the necrotic area of a rabbit model of ONFH to treat the disease. Four weeks later, micro-computed tomography (CT) quantitative analysis showed that 58.8±7.4% of the necrotic area was regenerated in the DMOG-treated ASCs transplantation group, 45.5±3.4% in normal ASCs transplantation group, 25.2±2.8% in only core decompression group and 10.6±2.6% in the untreated group. Histological analysis showed that transplantation of DMOG-treated ASCs clearly improved the bone regeneration of the necrotic area compared with the other three groups. Micro-CT and immunohistochemical analysis demonstrated the revasculation of the necrotic area were also increased significantly in the DMOG-treated ASC group compared with the control groups. Thus, it is hypothesized that DMOG could increase the bone repair capacity of ASCs through enhancing HIF-1α expression in the treatment of ONFH.

Targeting the hypoxic response in bone tissue engineering: A balance between supply and consumption to improve bone regeneration

Bone tissue engineering is a promising therapeutic alternative for bone grafting of large skeletal defects. It generally comprises an ex vivo engineered combination of a carrier structure, stem/progenitor cells and growth factors. However, the success of these regenerative implants largely depends on how well implanted cells will adapt to the hostile and hypoxic host environment they encounter after implantation. In this review, we will discuss how hypoxia signalling may be used to improve bone regeneration in a tissue-engineered construct. First, hypoxia signalling induces angiogenesis which increases the survival of the implanted cells as well as stimulates bone formation. Second, hypoxia signalling has also angiogenesis-independent effects on mesenchymal cells in vitro, offering exciting new possibilities to improve tissue-engineered bone regeneration in vivo. In addition, studies in other fields have shown that benefits of modulating hypoxia signalling include enhanced cell survival, proliferation and differentiation, culminating in a more potent regenerative implant. Finally, the stimulation of endochondral bone formation as a physiological pathway to circumvent the harmful effects of hypoxia will be briefly touched upon. Thus, angiogenic dependent and independent processes may counteract the deleterious hypoxic effects and we will discuss several therapeutic strategies that may be combined to withstand the hypoxia upon implantation and improve bone regeneration.

Protective effect of salidroside against bone loss via hypoxia-inducible factor-1α pathway-induced angiogenesis

Hypoxia-inducible factor (HIF)-1α plays a critical role in coupling angiogenesis with osteogenesis during bone development and regeneration. Salidroside (SAL) has shown anti-hypoxic effects in vitro and in vivo. However, the possible roles of SAL in the prevention of hypoxia-induced osteoporosis have remained unknown. Two osteoblast cell lines, MG-63 and ROB, were employed to evaluate the effects of SAL on cell viability, apoptosis, differentiation and mineralization in vitro. Rats subjected to ovariectomy-induced bone loss were treated with SAL in vivo. Our results showed that pre-treatment with SAL markedly attenuated the hypoxia-induced reductions in cell viability, apoptosis, differentiation and mineralization. SAL down-regulated HIF-1α expression and inhibited its translocation; however, SAL increased its transcriptional activity and, consequently, up-regulated vascular endothelial growth factor (VEGF). In vivo studies further demonstrated that SAL caused decreases in the mineral, alkaline phosphatase (ALP), and BGP concentrations in the blood of ovariectomized (OVX) rats. Moreover, SAL improved the trabecular bone microarchitecture and increased bone mineral density in the distal femur. Additionally, SAL administration partially ameliorated this hypoxia via the HIF-1α-VEGF signalling pathway. Our results indicate that SAL prevents bone loss by enhancing angiogenesis and osteogenesis and that these effects are associated with the activation of HIF-1α signalling.

Harnessing gene and drug delivery for vascularizing engineered tissue platforms

Enhancement of tissue vascularization is a therapeutic target for many ischemic conditions, and is crucial for successful engraftment of therapeutic cells for tissue regeneration. The authors present opportunities for using these platforms for dissecting the role of angiogenic mechanisms and highlight recent gene and drug delivery strategies for enhancing vascularization of engineered tissues. Modular tissue engineering is featured as an example.

Exosomes Secreted by Human-Induced Pluripotent Stem Cell-Derived Mesenchymal Stem Cells Repair Critical-Sized Bone Defects through Enhanced Angiogenesis and Osteogenesis in Osteoporotic Rats

Bone defects caused by trauma, severe infection, tumor resection and skeletal abnormalities are common osteoporotic conditions and major challenges in orthopedic surgery, and there is still no effective solution to this problem. Consequently, new treatments are needed to develop regeneration procedures without side effects. Exosomes secreted by mesenchymal stem cells (MSCs) derived from human induced pluripotent stem cells (hiPSCs, hiPSC-MSC-Exos) incorporate the advantages of both MSCs and iPSCs with no immunogenicity. However, there are no reports on the application of hiPSC-MSC-Exos to enhance angiogenesis and osteogenesis under osteoporotic conditions. HiPSC-MSC-Exos were isolated and identified before use. The effect of hiPSC-MSC-Exos on the proliferation and osteogenic differentiation of bone marrow MSCs derived from ovariectomized (OVX) rats (rBMSCs-OVX) in vitro were investigated. In vivo, hiPSC-MSC-Exos were implanted into critical size bone defects in ovariectomized rats, and bone regeneration and angiogenesis were examined by microcomputed tomography (micro-CT), sequential fluorescent labeling analysis, microfil perfusion and histological and immunohistochemical analysis. The results in vitro showed that hiPSC-MSC-Exos enhanced cell proliferation and alkaline phosphatase (ALP) activity, and up-regulated mRNA and protein expression of osteoblast-related genes in rBMSCs-OVX. In vivo experiments revealed that hiPSC-MSC-Exos dramatically stimulated bone regeneration and angiogenesis in critical-sized calvarial defects in ovariectomized rats. The effect of hiPSC-MSC-Exos increased with increasing concentration. In this study, we showed that hiPSC-MSC-Exos effectively stimulate the proliferation and osteogenic differentiation of rBMSCs-OVX, with the effect increasing with increasing exosome concentration. Further analysis demonstrated that the application of hiPSC-MSC-Exos+β-TCP scaffolds promoted bone regeneration in critical-sized calvarial defects by enhancing angiogenesis and osteogenesis in an ovariectomized rat model.

Dimethyloxaloylglycine Promotes the Angiogenic Activity of Mesenchymal Stem Cells Derived from iPSCs via Activation of the PI3K/Akt Pathway for Bone Regeneration

The vascularization of tissue-engineered bone is a prerequisite step for the successful repair of bone defects. Hypoxia inducible factor-1α (HIF-1α) plays an essential role in angiogenesis-osteogenesis coupling during bone regeneration and can activate the expression of angiogenic factors in mesenchymal stem cells (MSCs). Dimethyloxaloylglycine (DMOG) is an angiogenic small molecule that can inhibit prolyl hydroxylase (PHD) enzymes and thus regulate the stability of HIF-1α in cells at normal oxygen tension. Human induced pluripotent stem cell-derived MSCs (hiPSC-MSCs) are promising alternatives for stem cell therapy. In this study, we evaluated the effect of DMOG on promoting hiPSC-MSCs angiogenesis in tissue-engineered bone and simultaneously explored the underlying mechanisms in vitro. The effectiveness of DMOG in improving the expression of HIF-1α and its downstream angiogenic genes in hiPSC-MSCs demonstrated that DMOG significantly enhanced the gene and protein expression profiles of angiogenic-related factors in hiPSC-MSCs by sustaining the expression of HIF-1α. Further analysis showed that DMOG-stimulated hiPSC-MSCs angiogenesis was associated with the phosphorylation of protein kinase B (Akt) and with an increase in VEGF production. The effects could be blocked by the addition of the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002. In a critical-sized calvarial defect model in rats, DMOG-treated hiPSC-MSCs showed markedly improved angiogenic capacity in the tissue-engineered bone, leading to bone regeneration. Collectively, the results indicate that DMOG, via activation of the PI3K/Akt pathway, promotes the angiogenesis of hiPSC-MSCs in tissue-engineered bone for bone defect repair and that DMOG-treated hiPSC-MSCs can be exploited as a potential therapeutic tool in bone regeneration.

Advantages of pure platelet-rich plasma compared with leukocyte- and platelet-rich plasma in promoting repair of bone defects

Background

High levels of pro-inflammatory cytokines in leukocyte- and platelet-rich plasma (L-PRP) may activate the nuclear factor κB (NF-κB) pathway to counter the beneficial effect of the growth factors on bone regeneration. However, to date, no relevant studies have substantiated this.

Methods

L-PRP and pure platelet-rich plasma (P-PRP) were isolated. The in vitro effects of L-PRP and P-PRP on the proliferation, viability and migration of human bone marrow-derived mesenchymal stem cells (HBMSCs) and EaHy926, tube formation of EaHy926, and osteogenic differentiation of HBMSCs were assessed by cell counting, flow cytometry, scratch assay, tube formation assay, and real-time quantitative polymerase chain reaction (RT-PCR), western blotting and Alizarin red staining, respectively. The in vitro effects of L-PRP and P-PRP on the nuclear translocation of NF-κB p65, mRNA expression of inducible nitric oxide synthase and cyclooxygenase-2, and production of prostaglandin E2 and nitric oxid were assessed by western blotting, RT-PCR, enzyme-linked immunosorbent assay and Griess reaction, respectively. The in vivo effects of L-PRP or P-PRP preprocessed β-tricalcium phosphate (β-TCP) on the calvarial defects in rats were assessed by histological and immunofluorescence examinations.

Results

P-PRP, which had similar platelet and growth factors concentrations but significantly lower concentrations of leukocytes and pro-inflammatory cytokines compared with L-PRP, promoted the proliferation, viability and migration of HBMSCs and EaHy926, tube formation of EaHy926 and osteogenic differentiation of HBMSCs in vitro, compared with L-PRP. The implantation of P-PRP preprocessed β-TCP also yielded better histological results than the implantation of L-PRP preprocessed β-TCP in vivo. Moreover, L-PRP treatment resulted in the activation of the NF-κB pathway in HBMSCs and EaHy926 in vitro while the postoperative delivery of caffeic acid phenethyl ester, an inhibitor of NF-κB activation, enhanced the histological results of the implantation of L-PRP preprocessed β-TCP in vivo.

Conclusions

Leukocytes in L-PRP may activate the NF-κB pathway via the increased pro-inflammatory cytokines to induce the inferior effects on bone regeneration of L-PRP compared with P-PRP. Hence, P-PRP may be more suitable for bone regeneration compared with L-PRP, and the combined use of P-PRP and β-TCP represents a safe, simple, and effective alternative option for autogenous bone graft in the treatment of bone defects.

Three-dimensional poly (ε-caprolactone)/hydroxyapatite/collagen scaffolds incorporating bone marrow mesenchymal stem cells for the repair of bone defects

We previously demonstrated that three-dimensional (3D) hydroxyapatite (HAP)-collagen (COL)-coated poly(ε-caprolactone) (PCL) scaffolds (HAP-COL-PCL) possess appropriate nano-structures, surface roughness, and nutrients, providing a favorable environment for osteogenesis. However, the effect of using 3D HAP-COL-PCL scaffolds incorporating BMSCs for the repair of bone defects in rats has been not evaluated. 3D PCL scaffolds coated with HAP, collagen or HAP/COL and incorporating BMSCs were implanted into calvarial defects. At 12 weeks after surgery, the rats were sacrificed and crania were harvested to assess the bone defect repair using microcomputed tomography (micro-CT), histology, immunohistochemistry and sequential fluorescent labeling analysis. 3D micro-CT reconstructed images and quantitative analysis showed that HAP-COL-PCL groups possessed better bone-forming capacity than HAP-PCL groups or COL-PCL groups. Fluorescent labeling analysis revealed the percentage of tetracycline labeling, alizarin red labeling, and calcein labeling in HAP-COL-PCL groups were all greater than in the other two groups (P < 0.05), and the result was confirmed by immunohistochemical staining and histological analysis of bone regeneration. This study demonstrates that 3D HAP-COL-PCL scaffolds incorporating BMSCs markedly enhance bone regeneration of bone defects in rats.

Characterization of bone marrow-derived mesenchymal stem cells from dimethyloxallyl glycine-preconditioned mice: Evaluation of the feasibility of dimethyloxallyl glycine as a mobilization agent

The prolyl hydroxylase inhibitor dimethyloxallyl glycine (DMOG) has been increasingly studied with regards to stem cell therapy. Previous studies have demonstrated that endogenous mesenchymal stem cells (MSCs) may be mobilized into peripheral circulation by pharmaceutical preconditioning. In addition, our previous study confirmed that DMOG, as a novel mobilization agent, could induce mouse/rat MSC migration into peripheral blood circulation. Therefore, the present study conducted studies to characterize bone marrow-derived MSCs (BM-MSCs) collected from mice following DMOG intraperitoneal injection. The surface antigen immune phenotype, differentiation capability, proliferative ability, migratory capacity and paracrine capacity of the BM-MSCs collected from DMOG-preconditioned mice (DBM-MSCs) or normal saline-treated mice (NBM-MSCs) were evaluated by means of flow cytometry, differentiation induction, Cell Counting kit-8, Transwell assay and enzyme-linked immunosorbent assay, respectively. Compared with NBM-MSCs, DBM-MSCs displayed a similar immune phenotype and multilineage differentiation capability, reduced proliferative ability and migratory capacity, and similar transforming growth factor and platelet-derived growth factor secretion capacity. These results provide a novel insight into the biological properties of BM-MSCs from mice preconditioned with DMOG. DBM-MSCs exhibited slightly distinct characteristics to NBM-MSCs; however, they may have therapeutic potential for future stem cell therapy. In addition, the present study suggested that DMOG may be used as a novel mobilization agent in future clinical trials as no adverse effects were observed.

Prolonged exposure to hypoxic milieu improves the osteogenic potential of adipose derived stem cells

Mesenchymal stem cells (MSC) have been widely used in orthopedics for several applications. Conventionally, MSC are maintained under 21% O2 which does not reflect the real O2 tension in vivo. Recently, it was reported that different O2 conditions can give different cellular responses. Here, we investigated whether prolonged exposure to hypoxia affects the osteogenic differentiation of adipose-derived stem cells (ASC). ASC from six individuals were cultured under "low" (2-3%) or "air" (21%) oxygen tensions, either without or with osteogenic stimuli. The effect of the O2 tension was evaluated on cell proliferation, surface antigens, stemness and bone-related genes expression, alkaline phosphatase activity (ALP), mineralization activity, and release of osteogenic growth factors. Without differentiating stimuli, hypoxia favored ASC proliferation, reduced the number of CD184+ and CD34+ cells, and preserved the expression of NANOG and SOX2. The combination of hypoxia and osteogenic medium induced a high proliferation rate, a rapid and more pronounced mineralization activity, a higher expression of genes related to the MSC differentiation, a higher release of mitogenic growth factors (bFGF, PDGF-BB), and the decrease in TGF-β secretion, an inhibitor of the early stage of the osteoblast differentiation. We demonstrated that hypoxia acts dually, favoring ASC proliferation and the maintenance of the stemness in the absence of osteogenic stimuli, but inducing the differentiation in a bone-like microenvironment. In conclusion, prolonged cell culture in hypoxic microenvironment represents a proper method to modulate the stem cell function that may be used in several applications, for example, studies on bone pathophysiology or bone-tissue engineering.

Prolyl hydroxylase inhibitors act as agents to enhance the efficiency of cell therapy

INTRODUCTION

In stem cell-based therapy as a subtype of regenerative medicine, stem cells can be used to replace or repair injured tissue and cells in order to treat disease. Stem cells have the ability to integrate into injured areas and produce new cells via processes of proliferation and differentiation. Several studies have demonstrated that hypoxia increases self-renewal, proliferation and post-homing differentiation of stem cells through the regulation of hypoxia-inducible factor-1 (HIF-1)-mediated gene expression. Thus, pharmacological interventions including prolyl hydroxylase (PHD) inhibitors are considered as promising solutions for stem cell-based therapy. PHD inhibitors stabilize the HIF-1 and activate its pathway through preventing proteasomal degradation of HIF-1.

AREAS COVERED

This review focuses on the role of hypoxia, HIF-1 and especially PHD inhibitors on cell therapy. PHD structure and function are discussed as well as their inhibitors. In addition, we have investigated several preclinical studies in which PHD inhibitors improved the efficiency of cell-based therapies.

EXPERT OPINION

The data reviewed here suggest that PHD inhibitors are effective operators in improving stem cell therapy. However, because of some limitations, these compounds should be properly examined before clinical application.

Stimulation of osteogenesis and angiogenesis of hBMSCs by delivering Si ions and functional drug from mesoporous silica nanospheres

Multifunctional bioactive materials with the ability to stimulate osteogenesis and angiogenesis of stem cells play an important role in the regeneration of bone defects. However, how to develop such biomaterials remains a significant challenge. In this study, we prepared mesoporous silica nanospheres (MSNs) with uniform sphere size (∼90 nm) and mesopores (∼2.7 nm), which could release silicon ions (Si) to stimulate the osteogenic differentiation of human bone marrow stromal cells (hBMSCs) via activating their ALP activity, bone-related gene and protein (OCN, RUNX2 and OPN) expression. Hypoxia-inducing therapeutic drug, dimethyloxaloylglycine (DMOG), was effectively loaded in the mesopores of MSNs (D-MSNs). The sustained release of DMOG from D-MSNs could stabilize HIF-1α and further stimulated the angiogenic differentiation of hBMSCs as indicated by the enhanced VEGF secretion and protein expression. Our study revealed that D-MSNs could combine the stimulatory effect on both osteogenic and angiogenic activity of hBMSCs. The potential mechanism of D-MSN-stimulated osteogenesis and angiogenesis was further elucidated by the supplementation of cell culture medium with pure Si ions and DMOG. Considering the easy handling characteristics of nanospheres, the prepared D-MSNs may be applied in the forms of injectable spheres for minimally invasive surgery, or MSNs/polymer composite scaffolds for bone defect repair. The concept of delivering both stimulatory ions and functional drugs may offer a new strategy to construct a multifunctional biomaterial system for bone tissue regeneration.