Ticagrelor regulates osteoblast and osteoclast function and promotes bone formation in vivo via an adenosine-dependent mechanism

Clopidogrel protects against gentamicin-induced nephrotoxicity through targeting oxidative stress, apoptosis, and coagulation pathways

Gentamicin (Genta)-induced nephrotoxicity poses a significant clinical challenge due to its detrimental effects on kidney function. Clopidogrel (Clop), an antiplatelet drug known for its ability to prevent blood clots by inhibiting platelet aggregation, also has potential effects on oxidative stress and cell death. This study investigates Clop's protective role against Genta-induced nephrotoxicity, emphasizing the importance of the coagulation cascade. The 32 adult male albino rats were randomly assigned to four groups of eight (n = 8). The first group received only the vehicle. Genta was injected intraperitoneally at 100 mg/kg/day for 8 days in the second group. Groups 3 and 4 received oral Clop at 10 and 20 mg/kg/day for 1 week before Genta delivery and throughout the experiment. Renal tissue showed renal function tests, oxidative stress, pro-inflammatory cytokines, apoptotic markers, coagulation profile, and fibrin expression. Clop improved Genta-induced kidney function and histopathology. Clop substantially reduced pro-inflammatory cytokines, oxidative stress indicators, pro-apoptotic proteins, and fibrin protein. Clop also significantly boosted renal tissue anti-inflammatory and anti-apoptotic protein expression. Genta-induced nephrotoxicity involves oxidative stress, apoptosis, and coagulation system activation, according to studies. This study underscores that Genta-induced nephrotoxicity is associated with oxidative stress, apoptosis, and activation of the coagulation system. Clop's protective effects on nephrons are attributed to its anticoagulant, antioxidant, anti-inflammatory, and anti-apoptotic properties, presenting it as a promising therapeutic strategy against Genta-induced kidney damage.

Aspirin and Ticagrelor Versus Aspirin and Clopidogrel or Prasugrel and the Effect on Staphylococcal-associated Infections: A Real-world Study

PURPOSE

Antiplatelet therapy is used for the primary and secondary prevention of thrombotic diseases such as acute coronary syndrome (ACS). These patients are more vulnerable to infections, as such, strategies are required to mitigate these risks.

METHODS

We conducted a retrospective cohort study using TriNetX, a global federated health research network that includes both inpatient and outpatient electronic medical records from health care organizations worldwide. Patients ≥18 years old, after ACS, who were placed on aspirin and ticagrelor were compared with patients placed on aspirin and clopidogrel or prasugrel. Patients were identified using International Statistical Classification of Diseases and Related Health Problems terminology codes. After propensity score matching (1:1), a total of 239,358 patients were identified in each cohort. The primary outcomes of interest investigated were rates of (1) acute and subacute infective endocarditis, (2) sepsis of unknown origin, (3) staphylococcus arthritis, (4) cellulitis and acute lymphangitis, (5) Staphylococcus aureus bacteremia, and (6) staphylococcal pneumonia after initiation of treatment. Outcomes were analyzed at 1, 3, and 5 years.

FINDINGS

At 5 years, a combination of aspirin and ticagrelor, compared with a combination of aspirin and clopidogrel or prasugrel, was associated with significantly reduced rates of (1) acute and subacute endocarditis (hazard ratio [HR] plus 95% CI) (HR = 0.85; 0.77-0.945; P = 0.030), (2) sepsis of unknown origin (HR = 0.89; 95% CI, 0.86-0.91; P < 0.0001), (3) cellulitis and acute lymphangitis (HR = 0.89; 95% CI, 0.87-0.92; P < 0.0001, and (4) Staphylococcus aureus bacteremia (HR = 0.72; 95% CI, 0.61-0.85; P = 0.0007). However, a combination of aspirin and clopidogrel was associated with a marinally lower risk of staphylococcal pneumonia (HR = 1.04; 95% CI, 1.01-1.062; P < 0.0001).

IMPLICATIONS

A combination of aspirin and ticagrelor is associated with a lower rate of a variety of bacterial infections. This combination warrants further investigation in in-vitro studies to tease out mechanisms and through clinical randomized trials in groups who have ACS and are at high infection risk.

Translational Experimental Basis of Indirect Adenosine Receptor Agonist Stimulation for Bone Regeneration: A Review

Bone regeneration remains a significant clinical challenge, often necessitating surgical approaches when healing bone defects and fracture nonunions. Within this context, the modulation of adenosine signaling pathways has emerged as a promising therapeutic option, encouraging osteoblast activation and tempering osteoclast differentiation. A literature review of the PubMed database with relevant keywords was conducted. The search criteria involved in vitro or in vivo models, with clear methodological descriptions. Only studies that included the use of indirect adenosine agonists, looking at the effects of bone regeneration, were considered relevant according to the eligibility criteria. A total of 29 articles were identified which met the inclusion and exclusion criteria, and they were reviewed to highlight the preclinical translation of adenosine agonists. While preclinical studies demonstrate the therapeutic potential of adenosine signaling in bone regeneration, its clinical application remains unrealized, underscoring the need for further clinical trials. To date, only large, preclinical animal models using indirect adenosine agonists have been successful in stimulating bone regeneration. The adenosine receptors (A1, A2A, A2B, and A3) stimulate various pathways, inducing different cellular responses. Specifically, indirect adenosine agonists act to increase the extracellular concentration of adenosine, subsequently agonizing the respective adenosine receptors. The agonism of each receptor is dependent on its expression on the cell surface, the extracellular concentration of adenosine, and its affinity for adenosine. This comprehensive review analyzed the multitude of indirect agonists currently being studied preclinically for bone regeneration, discussing the mechanisms of each agonist, their cellular responses in vitro, and their effects on bone formation in vivo.

Regulatory T cell-derived exosome mediated macrophages polarization for osteogenic differentiation in fracture repair

Refractory fracture presents an intractable challenge in trauma treatment. Selective polarization of macrophages as well as the recruitment of osteogenic precursor cells play key roles in osteogenic differentiation during fracture healing. Here we constructed regulatory T cell (Treg)-derived exosomes (Treg-Exo) for the treatment of fracture. The obtained exosomes displayed a spheroid shape with a hydrated particle size of approximately 130 nm. With further purification using CD39 and CD73 antibody-modified microfluidic chips, CD39 and CD73 specifically expressing exosomes were obtained. This kind of Treg-Exo utilized the ectonucleotidases of CD39 and CD73 to catalyze the high level of ATP in the fracture area into adenosine. The generated adenosine further promoted the selective polarization of macrophages. When interacting with mesenchymal stem cells (MSCs, osteogenic precursor cells), both Treg-Exo and Treg-Exo primed macrophages facilitated the proliferation and differentiation of MSCs. After administration in vivo, Treg-Exo effectively promoted fracture healing compared with conventional T cell-derived exosome. To further improve the delivery efficacy of exosomes and integrate multiple biological processes of fracture healing, an injectable hydrogel was fabricated to co-deliver Treg-Exo and stromal cell-derived factor 1 alpha (SDF-1α). With the dual effect of Treg-Exo for macrophage polarization and SDF-1α for MSC recruitment, the multifunctional hydrogel exerted a synergistic effect on fracture repair acceleration. This study provided a promising therapeutic candidate and synergistic strategy for the clinical treatment of fracture.

Ticagrelor was associated with lower fracture risk than clopidogrel in the dual anti-platelet regimen among patients with acute coronary syndrome treated with percutaneous coronary intervention

PURPOSE

Patients with coronary artery disease have increased fracture risks. P2Y12 inhibitors may impact fracture risks. We compared the fracture risks associated with ticagrelor and clopidogrel in dual anti-platelet therapy (DAPT).

METHODS

We identified all adults who underwent first-ever percutaneous coronary intervention (PCI) for acute coronary syndrome (ACS) between 2010 and 2017 from a territory-wide PCI registry in Hong Kong. Following 1:1 propensity-score matching for baseline characteristics, patients were followed up till event occurrence, death, or 30 June 2022. Outcomes of interest were major osteoporotic fractures (MOF) identified by validated ICD-9-CM codes. Cox proportional hazards regression was used to compute the hazard ratio (HR) for MOF associated with ticagrelor versus clopidogrel use.

RESULTS

3018 ticagrelor users and 3018 clopidogrel users were identified after propensity-score matching (mean age: 61.4 years; 84.1% men). Upon median follow-up of 6.5 years, 59 ticagrelor users and 119 clopidogrel users sustained MOF (annualized fracture risks: 0.34% and 0.56%, respectively). Ticagrelor use was associated with lower risks of MOF (HR 0.60, 95%CI 0.44-0.83; p = 0.002). Consistent HRs were observed for fractures over vertebrae, hip and upper limbs. Subgroup analyses showed no interaction according to age, sex, presence of diabetes, presence of chronic kidney disease and prior fracture history.

CONCLUSION

Among adults who underwent first-ever PCI for ACS, ticagrelor use in the DAPT was associated with a lower risk of MOF compared with clopidogrel. Our results support the use of ticagrelor in the DAPT from the perspective of bone health.

Amino acid-based supramolecular chiral hydrogels promote osteogenesis of human dental pulp stem cells via the MAPK pathway

Critical-size defects (CSDs) of the craniofacial bones cause aesthetic and functional complications that seriously impact the quality of life. The transplantation of human dental pulp stem cells (hDPSCs) is a promising strategy for bone tissue engineering. Chirality is commonly observed in natural biomolecules, yet its effect on stem cell differentiation is seldom studied, and little is known about the underlying mechanism. In this study, supramolecular chiral hydrogels were constructed using L/d-phenylalanine (L/D-Phe) derivatives. The results of alkaline phosphatase expression analysis, alizarin red S assay, as well as quantitative real-time polymerase chain reaction and western blot analyses suggest that right-handed D-Phe hydrogel fibers significantly promoted osteogenic differentiation of hDPSCs. A rat model of calvarial defects was created to investigate the regulation of chiral nanofibers on the osteogenic differentiation of hDPSCs in vivo. The results of the animal experiment demonstrated that the D-Phe group exhibited greater and faster bone formation on hDPSCs. The results of RNA sequencing, vinculin immunofluorescence staining, a calcium fluorescence probe assay, and western blot analysis indicated that L-Phe significantly promoted adhesion of hDPSCs, while D-Phe nanofibers enhanced osteogenic differentiation of hDPSCs by facilitating calcium entry into cells and activate the MAPK pathway. These results of chirality-dependent osteogenic differentiation offer a novel therapeutic strategy for the treatment of CSDs by optimising the differentiation of hDPSCs into chiral nanofibers.

The Effect of Clopidogrel and Ticagrelor on Human Adipose Mesenchymal Stem Cell Osteogenic Differentiation Potential: In Vitro Comparative Study

Ticagrelor (TICA) and clopidogrel (CLP) are extensively used antiplatelet drugs that act by antagonizing the P2Y12 receptors that are found on platelets in addition to bone cells. Aim. The purpose of this study was to investigate the effect of clopidogrel and ticagrelor on stem cells osteogenic differentiation in vitro. Methods. Human adipose-derived mesenchymal stem cells (hAd-MSCs) were divided into (1) control group, (2) osteogenic group (osteo group), (3) clopidogrel group (CLP group), and (4) ticagrelor group (TICA group). The osteogenic differentiation potential was determined by mineralization nodule formation using Alizarin Red S staining, measuring ALP enzyme activity by alkaline phosphatase assay. Quantitative determination for osteogenic markers included osteocalcin (OC); runt-related transcription factor 2 (RUNX2) performed using western blot; osteoprotegerin (OPG) using enzyme-linked immunosorbent assay (ELISA) and inflammatory markers; and tumor necrosis factor (TNF-α) and interleukin-6 (IL-6) measured using real-time polymerase chain reaction quantitative (RT-PCR) and ELISA. Results. In comparison to all study groups, the TICA group showed significant increase in the mineralized extracellular matrix, ALP enzyme activity, and bone markers expression as RUNX2 (P < 0.0001), OC, and OPG (P < 0.05). The expression of IL-6 and TNF-α was determined by RT-qPCR and ELISA techniques. TICA and CLP significantly decreased both markers compared to the control group. The TICA group showed statistically significant lower levels of both markers (P < 0.0001) than the CLP and control groups via the ELISA technique. Conclusion. TICA may possess a positive effect on hAd-MSCs osteogenic differentiation compared to CLP.

Effect of direct oral anticoagulant dabigatran on early bone healing: An experimental study in rats

Background

Dabigatran belongs to the new generation of direct oral anticoagulants (DOACs). Its advantages are oral administration and no need for international normalized ratio (INR) monitoring. Although its use has increased, its potential side effects on bone healing and remodeling have not been fully investigated. The present study aimed to evaluate the possible effects of dabigatran on early bone healing.

Methods

Sixteen male Wistar rats were divided into two groups; in group A, 20-mg/kg dabigatran dose was administered orally daily for 15 days, while group B served as a control. Two circular bone defects (d=6 mm) were created on either side of the parietal bones. Two weeks after surgery and euthanasia of the animals, tissue samples (parietal bones that contained the defects) were harvested for histological and histomorphometric analysis. Statistical analysis was performed with a significance level of α=0.5.

Results

No statistically significant differences were found between the two groups regarding the regenerated bone (21.9% vs. 16.3%, P=0.172) or the percentage of bone bridging (63.3% vs. 53.5%, P=0.401).

Conclusion

Dabigatran did not affect bone regeneration, suggesting that it might be a safer drug compared to older anticoagulants known to lead to bone healing delay.

Bone Tissue Engineering (BTE) of the Craniofacial Skeleton, Part I: Evolution and Optimization of 3D-Printed Scaffolds for Repair of Defects

Bone tissue regeneration is a complex process that proceeds along the well-established wound healing pathway of hemostasis, inflammation, proliferation, and remodeling. Recently, tissue engineering efforts have focused on the application of biological and technological principles for the development of soft and hard tissue substitutes. Aim is directed towards boosting pathways of the healing process to restore form and function of tissue deficits. Continued development of synthetic scaffolds, cell therapies, and signaling biomolecules seeks to minimize the need for autografting. Despite being the current gold standard treatment, it is limited by donor sites' size and shape, as well as donor site morbidity. Since the advent of computer-aided design/computer-aided manufacturing (CAD/CAM) and additive manufacturing (AM) techniques (3D printing), bioengineering has expanded markedly while continuing to present innovative approaches to oral and craniofacial skeletal reconstruction. Prime examples include customizable, high-strength, load bearing, bioactive ceramic scaffolds. Porous macro- and micro-architecture along with the surface topography of 3D printed scaffolds favors osteoconduction and vascular in-growth, as well as the incorporation of stem and/or other osteoprogenitor cells and growth factors. This includes platelet concentrates (PCs), bone morphogenetic proteins (BMPs), and some pharmacological agents, such as dipyridamole (DIPY), an adenosine A 2A receptor indirect agonist that enhances osteogenic and osteoinductive capacity, thus improving bone formation. This two-part review commences by presenting current biological and engineering principles of bone regeneration utilized to produce 3D-printed ceramic scaffolds with the goal to create a viable alternative to autografts for craniofacial skeleton reconstruction. Part II comprehensively examines recent preclinical data to elucidate the potential clinical translation of such 3D-printed ceramic scaffolds.

A Machine Learning-Based Image Segmentation Method to Quantify In Vitro Osteoclast Culture Endpoints

Quantification of in vitro osteoclast cultures (e.g. cell number) often relies on manual counting methods. These approaches are labour intensive, time consuming and result in substantial inter- and intra-user variability. This study aimed to develop and validate an automated workflow to robustly quantify in vitro osteoclast cultures. Using ilastik, a machine learning-based image analysis software, images of tartrate resistant acid phosphatase-stained mouse osteoclasts cultured on dentine discs were used to train the ilastik-based algorithm. Assessment of algorithm training showed that osteoclast numbers strongly correlated between manual- and automatically quantified values (r = 0.87). Osteoclasts were consistently faithfully segmented by the model when visually compared to the original reflective light images. The ability of this method to detect changes in osteoclast number in response to different treatments was validated using zoledronate, ticagrelor, and co-culture with MCF7 breast cancer cells. Manual and automated counting methods detected a 70% reduction (p < 0.05) in osteoclast number, when cultured with 10 nM zoledronate and a dose-dependent decrease with 1-10 μM ticagrelor (p < 0.05). Co-culture with MCF7 cells increased osteoclast number by ≥ 50% irrespective of quantification method. Overall, an automated image segmentation and analysis workflow, which consistently and sensitively identified in vitro osteoclasts, was developed. Advantages of this workflow are (1) significantly reduction in user variability of endpoint measurements (93%) and analysis time (80%); (2) detection of osteoclasts cultured on different substrates from different species; and (3) easy to use and freely available to use along with tutorial resources.

Employing Indirect Adenosine 2A Receptors (A2AR) to Enhance Osseointegration of Titanium Devices: A Pre-Clinical Study

The present study aimed to evaluate the effect of dipyridamole, an indirect adenosine 2A receptors (A_2AR), on the osseointegration of titanium implants in a large, translational pre-clinical model. Sixty tapered, acid-etched titanium implants, treated with four different coatings ((i) Type I Bovine Collagen (control), (ii) 10 μM dipyridamole (DIPY), (iii) 100 μM DIPY, and (iv) 1000 μM DIPY), were inserted in the vertebral bodies of 15 female sheep (weight ~65 kg). Qualitative and quantitative analysis were performed after 3, 6, and 12 weeks in vivo to assess histological features, and percentages of bone-to-implant contact (%BIC) and bone area fraction occupancy (%BAFO). Data was analyzed using a general linear mixed model analysis with time in vivo and coating as fixed factors. Histomorphometric analysis after 3 weeks in vivo revealed higher BIC for DIPY coated implant groups (10 μM (30.42% ± 10.62), 100 μM (36.41% ± 10.62), and 1000 μM (32.46% ± 10.62)) in comparison to the control group (17.99% ± 5.82). Further, significantly higher BAFO was observed for implants augmented with 1000 μM of DIPY (43.84% ± 9.97) compared to the control group (31.89% ± 5.46). At 6 and 12 weeks, no significant differences were observed among groups. Histological analysis evidenced similar osseointegration features and an intramembranous-type healing pattern for all groups. Qualitative observation corroborated the increased presence of woven bone formation in intimate contact with the surface of the implant and within the threads at 3 weeks with increased concentrations of DIPY. Coating the implant surface with dipyridamole yielded a favorable effect with regard to BIC and BAFO at 3 weeks in vivo. These findings suggest a positive effect of DIPY on the early stages of osseointegration.

Extracellular adenosine signaling in bone health and disease

Purinergic signaling is a key molecular pathway in the maintenance of bone health and regeneration. P1 receptor signaling, which is activated by extracellular adenosine, has emerged as a key metabolic pathway that regulates bone tissue formation, function, and homeostasis. Extracellular adenosine is mainly produced by ectonucleotidases, and alterations in the function of these enzymes or compromised adenosine generation can result in bone disorders, such as osteoporosis and impaired fracture healing. This mini review discusses the key role played by adenosine in bone health and how its alterations contribute to bone diseases, as well as potential therapeutic applications of exogenous adenosine to combat bone diseases like osteoporosis and injury.

The Function and Regulation of Platelet P2Y12 Receptor

In addition to the key role in hemostasis and thrombosis, platelets have also been wildly acknowledged as immune regulatory cells and involving in the pathogenesis of inflammation-related diseases. Since purine receptor P2Y12 plays a crucial role in platelet activation, P2Y12 antagonists such as clopidogrel, prasugrel, and ticagrelor have been widely used in cardiovascular diseases worldwide in recent decades due to their potent antiplatelet and antithrombotic effects. Meanwhile, the role of P2Y12 in inflammatory diseases has also been extensively studied. Relatively, there are few studies on the regulation of P2Y12. This review first summarizes the various roles of P2Y12 in the process of platelet activation, as well as downstream effects and signaling pathways; then introduces the effects of P2Y12 in inflammatory diseases such as sepsis, atherosclerosis, cancer, autoimmune diseases, and asthma; and finally reviews the current researches on P2Y12 regulation.

Novel alendronate-CGS21680 conjugate reduces bone resorption and induces new bone formation in post-menopausal osteoporosis and inflammatory osteolysis mouse models

Loss of bone is a common medical problem and, while it can be treated with available therapies, some of these therapies have critical side effects. We have previously demonstrated that CGS21680, a selective A2A adenosine receptor agonist, prevents bone loss, but its on-target toxicities (hypotension, tachycardia) and frequent dosing requirements make it unusable in the clinic. We therefore generated a novel alendronate-CGS21680 conjugate (MRS7216), to target the agonist to bone where it remains for long periods thereby diminishing the frequency of administration and curtailing side effects. MRS7216 was synthesized from CGS21680 by sequential activation of the carboxylic acid moiety and reacting with an appropriate amino acid (PEG, alendronic acid) under basic conditions. MRS7216 was tested on C57BL/6J (WT) mice with established osteoporosis (OP) and WT or A2A KO mice with wear particle-induced inflammatory osteolysis (OL). Mice were treated weekly with MRS7216 (10mg/kg). Bone formation was studied after in vivo labeling with calcein/Alizarin Red, and μCT and histology analyses were performed. In addition, human primary osteoblasts and osteoclasts were cultured using bone marrow discarded after hip replacement. Receptor binding studies demonstrate that MRS7216 efficiently binds the A2A adenosine receptor. MRS7216-treated OP and OL mice had significant new bone formation and reduced bone loss compared to vehicle or alendronate-treated mice. Histological analysis showed that MRS7216 treatment significantly reduced osteoclast number and increased osteoblast number in murine models. Interestingly, cultured human osteoclast differentiation was inhibited, and osteoblast differentiation was stimulated by the compound indicating that MRS7216 conjugates represent a novel therapeutic approach to treat osteoporosis and osteolysis.

Evaluation of the Effects of Dual Antiplatelet Therapy on Guided Bone Regeneration in Peri-Implant Bone Defect

In this study, the authors aim to investigate the effect of dual antiplatelet agents on peri-implant-guided bone regeneraation by studying a sample of rats with titanium implants in their tibias. The rats were randomly divided into 5 groups: acetylsalicylic acid (ASA) (n=10), treated with 20 mg/kg of ASA; ASA+CLPD (Clopidogrel): (n=10), treated with 20 mg/kg of ASA and 30 mg/kg of clopidogrel; ASA+PRSG (Prasugrel): (n=10), treated with 20 mg/kg of ASA and 15 mg/kg of prasugrel; ASA+TCGR (Ticagrelor): (n=10), treated with 20 mg/kg of ASA and 300 mg/kg of ticagrelor; and a control group (n=10) received no further treatment after implant surgery. Bone defects created half of the implant length circumferencial after implant insertion and defects filled with bone grafts. After 8 weeks experimental period, the rats sacrified and implants with surrounding bone tissues were collected to histologic analysis; bone filling ratios of defects (%) and blood samples collected to biochemical analysis (urea, creatinine, aspartate aminotransferase, alanine aminotransferase, phosphorus, magnesium, alkaline phosphatase, calcium, and parathormone). A statistically significant difference was not detected between the groups for all parameters (P>0.05). When the percentage of new bone formation was examined, it was found that there was no statistically significant difference between the groups (P>0.05). Antiplatelet therapy may not adversely affect guided bone regeneration in peri-implant bone defects.

P2Y12 inhibitor clopidogrel inhibits renal fibrosis by blocking macrophage-to-myofibroblast transition

Clopidogrel, a P2Y12 inhibitor, is a novel anti-fibrosis agent for chronic kidney disease (CKD), but its mechanisms remain unclear, which we investigated by silencing P2Y12 or treating unilateral ureteral obstruction (UUO) in LysM-Cre/Rosa Tomato mice with clopidogrel in vivo and in vitro. We found that P2Y12 was significantly increased and correlated with progressive renal fibrosis in CKD patients and UUO mice. Phenotypically, up to 82% of P2Y12-expressing cells within the fibrosing kidney were of macrophage origin, identified by co-expressing CD68/F4/80 antigens or a macrophage-lineage-tracing marker Tomato. Unexpectedly, more than 90% of P2Y12-expressing macrophages were undergoing macrophage-to-myofibroblast transition (MMT) by co-expressing alpha smooth muscle actin (α-SMA), which was also confirmed by single-cell RNA sequencing. Functionally, clopidogrel improved the decline rate of the estimated glomerular filtration rate (eGFR) in patients with CKD and significantly inhibited renal fibrosis in UUO mice. Mechanistically, P2Y12 expression was induced by transforming growth factor β1 (TGF-β1) and promoted MMT via the Smad3-dependent mechanism. Thus, silencing or pharmacological inhibition of P2Y12 was capable of inhibiting TGF-β/Smad3-mediated MMT and progressive renal fibrosis in vivo and in vitro. In conclusion, P2Y12 is highly expressed by macrophages in fibrosing kidneys and mediates renal fibrosis by promoting MMT via TGF-β/Smad3 signaling. Thus, P2Y12 inhibitor maybe a novel and effective anti-fibrosis agent for CKD.

Extracellular ATP and its derivatives provide spatiotemporal guidance for bone adaptation to wide spectrum of physical forces

ATP is a ubiquitous intracellular molecule critical for cellular bioenergetics. ATP is released in response to mechanical stimulation through vesicular release, small tears in cellular plasma membranes, or when cells are destroyed by traumatic forces. Extracellular ATP is degraded by ecto-ATPases to form ADP and eventually adenosine. ATP, ADP, and adenosine signal through purinergic receptors, including seven P2X ATP-gated cation channels, seven G-protein coupled P2Y receptors responsive to ATP and ADP, and four P1 receptors stimulated by adenosine. The goal of this review is to build a conceptual model of the role of different components of this complex system in coordinating cellular responses that are appropriate to the degree of mechanical stimulation, cell proximity to the location of mechanical injury, and time from the event. We propose that route and amount of ATP release depend on the scale of mechanical forces, ranging from vesicular release of small ATP boluses upon membrane deformation, to leakage of ATP through resealable plasma membrane tears, to spillage of cellular content due to destructive forces. Correspondingly, different P2 receptors responsive to ATP will be activated according to their affinity at the site of mechanical stimulation. ATP is a small molecule that readily diffuses through the environment, bringing the signal to the surrounding cells. ATP is also degraded to ADP which can stimulate a distinct set of P2 receptors. We propose that depending on the magnitude of mechanical forces and distance from the site of their application, ATP/ADP profiles will be different, allowing the relay of information about tissue level injury and proximity. Lastly, ADP is degraded to adenosine acting via its P1 receptors. The presence of large amounts of adenosine without ATP, indicates that an active source of ATP release is no longer present, initiating the transition to the recovery phase. This model consolidates the knowledge regarding the individual components of the purinergic system into a conceptual framework of choreographed responses to physical forces.

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Cellular bioenergetic molecule ATP is released when cell is mechanically stimulated.

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ATP release is proportional to the amount of cellular damage.

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ATP diffusion and transformation to ADP indicates the proximity to the damage.

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Purinergic receptors form a network choreographing cell response to physical forces.

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Complete transformation of ATP to adenosine initiates the recovery phase.

Pleiotropic effects of clopidogrel

Clopidogrel is a widely prescribed prodrug with anti-thrombotic activity through irreversible inhibition of the P2Y₁₂ receptor on platelets. It is FDA-approved for the clinical management of thrombotic diseases like unstable angina, myocardial infarction, stroke, and during percutaneous coronary interventions. Hepatic clopidogrel metabolism generates several distinct metabolites. Only one of these metabolites is responsible for inhibiting the platelet P2Y₁₂ receptor. Importantly, various non-hemostatic effects of clopidogrel therapy have been described. These non-hemostatic effects are perhaps unsurprising, as P2Y₁₂ receptor expression has been reported in multiple tissues, including osteoblasts, leukocytes, as well as vascular endothelium and smooth muscle. While the "inactive" metabolites have been commonly thought to be biologically inert, recent findings have uncovered P2Y₁₂ receptor-independent effects of clopidogrel treatment that may be mediated by understudied metabolites. In this review, we summarize both the P2Y₁₂ receptor-mediated and non-P2Y₁₂ receptor-mediated effects of clopidogrel and its metabolites in various tissues.

Association between osteoporosis or osteopenia and taking antiplatelet agents in general US population of NHANES

BACKGROUND

Osteoporosis (OP) and osteopenia are common bone disorders in old age, and lots of patients suffering from OP or osteopenia need to take antiplatelet agents to treat basic diseases. However, clinical data on the link between osteopenia or OP and antiplatelet agents are limited.

METHODS

Data in this study were collected and screened from the NHANES from 2013 to 2014 and 2017 to 2018. The variables were extracted from interviews and compared between OP or osteopenia participants and normal. The relationship between OP or osteopenia and taking antiplatelet drugs was analyzed by weighted multivariate logistic regression.

RESULTS

After excluding individuals who were not eligible and had invalid data, we finally identified 894 participants for inclusion in the study. We found a negative association between OP or osteopenia and taking antiplatelet agents (OR = 0.53; 95% CI, 0.33-0.84; p < 0.05). These results did not change on multiple imputations (OR = 0.32, 95% CI, 0.19-0.56; p <0.01). In the subgroup analyses, the associations were more significant in women (OR = 0.18, 95% CI, 0.05-0.62; p <0.05).

CONCLUSION

This study demonstrated that the association between OP or osteopenia and taking antiplatelet agents was significant. Therefore, it is necessary to confirm the result by extending further research.

Bone targeting nanocarrier-assisted delivery of adenosine to combat osteoporotic bone loss

Extracellular adenosine has been shown to play a key role in maintaining bone health and could potentially be used to treat bone loss. However, systemic administration of exogenous adenosine to treat bone disorders remains a challenge due to the ubiquitous presence of adenosine receptors in different organs and the short half-life of adenosine in circulation. Towards this, we have developed a bone-targeting nanocarrier and determined its potential for systemic administration of adenosine. The nanocarrier, synthesized via emulsion suspension photopolymerization, is comprised of hyaluronic acid (HA) copolymerized with phenylboronic acid (PBA), a moiety that can form reversible bonds with adenosine. The bone binding affinity of the nanocarrier was achieved by alendronate (Aln) conjugation. Nanocarriers functionalized with the alendronate (Aln-NC) showed a 45% higher accumulation in the mice vertebrae in vivo compared to those lacking alendronate molecules (NCs). Systemic administration of adenosine via bone-targeting nanocarriers (Aln-NC) attenuated bone loss in ovariectomized (OVX) mice. Furthermore, bone tissue of mice treated with adenosine-loaded Aln-NC displayed trabecular bone characteristics comparable to healthy controls as shown by microcomputed tomography, histochemical staining, bone labeling, and mechanical strength. Overall, our results demonstrate the use of a bone-targeting nanocarrier towards systemic administration of adenosine and its application in treating bone degenerative diseases such as osteoporosis.

Recent update on craniofacial tissue engineering

The craniofacial region consists of several different tissue types. These tissues are quite commonly affected by traumatic/pathologic tissue loss which has so far been traditionally treated by grafting procedures. With the complications and drawbacks of grafting procedures, the emerging field of regenerative medicine has proved potential. Tissue engineering advancements and the application in the craniofacial region is quickly gaining momentum although most research is still at early in vitro/in vivo stages. We aim to provide an overview on where research stands now in tissue engineering of craniofacial tissue; namely bone, cartilage muscle, skin, periodontal ligament, and mucosa. Abstracts and full-text English articles discussing techniques used for tissue engineering/regeneration of these tissue types were summarized in this article. The future perspectives and how current technological advancements and different material applications are enhancing tissue engineering procedures are also highlighted. Clinically, patients with craniofacial defects need hybrid reconstruction techniques to overcome the complexity of these defects. Cost-effectiveness and cost-efficiency are also required in such defects. The results of the studies covered in this review confirm the potential of craniofacial tissue engineering strategies as an alternative to avoid the problems of currently employed techniques. Furthermore, 3D printing advances may allow for fabrication of patient-specific tissue engineered constructs which should improve post-operative esthetic results of reconstruction. There are on the other hand still many challenges that clearly require further research in order to catch up with engineering of other parts of the human body.

Reduction in Osteoarthritis Risk After Treatment With Ticagrelor Compared to Clopidogrel: A Propensity Score-Matching Analysis

OBJECTIVE

Osteoarthritis (OA) is a common cause of joint pain and disability, and effective treatments are lacking. Extracellular adenosine has antiinflammatory effects and can prevent and treat OA in animal models. Ticagrelor and clopidogrel are both used in patients with coronary artery disease, but only ticagrelor increases extracellular adenosine levels. This study was undertaken to determine whether treatment with ticagrelor was associated with a lower risk of OA.

METHODS

We conducted a 1:2 propensity score-matching analysis using data from 2011-2017 in the Optum Clinformatics Data Mart. Patients who had received either ticagrelor or clopidogrel for ≥90 days were included in our study, and patients with a prior diagnosis of OA or inflammatory arthritis were excluded. OA was identified using International Classification of Diseases codes. The primary outcome was the time to diagnosis of OA after treatment with ticagrelor versus clopidogrel.

RESULTS

Our propensity score-matched cohort consisted of 7,007 ticagrelor-treated patients and 14,014 clopidogrel-treated patients, with a median number of days receiving treatment of 287 and 284, respectively. For both groups, the mean age was 64 years, and 73% of the patients were male. Multivariate Cox regression analysis estimated a hazard ratio for developing OA of 0.71 (95% confidence interval 0.64-0.79) (P < 0.001) after treatment with ticagrelor compared to clopidogrel.

CONCLUSION

Treatment with ticagrelor was associated with a 29% lower risk of developing OA compared to treatment with clopidogrel over 5 years of follow-up. We hypothesize that the reduction in OA seen in patients who received ticagrelor may in part be due to increased extracellular adenosine levels.

Polydopamine-assisted one-step modification of nanofiber surfaces with adenosine to tune the osteogenic differentiation of mesenchymal stem cells and the maturation of osteoclasts

Adenosine and its receptors have emerged as alternative targets to control cellular functions for bone healing. However, the soluble delivery of adenosine has not proven effective because of its fast degradation in vivo. We therefore designed a stable coating of adenosine for biomaterial surfaces through polydopamine chemistry to control osteogenesis and osteoclastogenesis via A2bR signaling. First, we prepared electrospun poly (ι-lactic acid) (PLLA) nanofiber sheets, which were modified through a one-step adenosine polydopamine coating process. Scanning electron microscopy (SEM) revealed deposition of particles on the adenosine polydopamine-coated PLLA (AP-PL) sheets compared to the polydopamine-only sheets. Moreover, X-ray photoelectron spectroscopy analysis confirmed an increase in nitrogen signals due to adenosine. Furthermore, adenosine loading efficiency and retention were significantly enhanced in AP-PL sheets compared to polydopamine-only sheets. Human adipose-derived stem cells (hADSCs) cultured on AP-PL expressed A2bR (1.30 ± 0.19 fold) at significantly higher levels than those cultured on polydopamine-only sheets. This in turn significantly elevated the expression of Runx2 (16.94 ± 1.68 and 51.69 ± 0.07 fold), OPN (1.63 ± 0.16 and 30.56 ± 0.25 fold), OCN (1.16 ± 0.13 and 5.23 ± 0.16 fold), and OSX (10.01 ± 0.81 and 62.48 ± 0.25 fold) in cells grown in growth media on days 14 and 21, respectively. Similarly, mineral deposition was enhanced to a greater extent in the AP-PL group than the polydopamine group, while blocking of A2bR significantly downregulated osteogenesis. Finally, osteoclast differentiation of RAW 264.7 cells was significantly inhibited by growth on AP-PL sheets. However, osteoclast differentiation was significantly stimulated after A2bR was blocked. Taken together, we propose that polydopamine-assisted one-step coating of adenosine is a viable method for surface modification of biomaterials to control osteogenic differentiation of stem cells and bone healing.

Role of UDP-Sugar Receptor P2Y14 in Murine Osteoblasts

The purinergic (P2) receptor P2Y₁₄ is the only P2 receptor that is stimulated by uridine diphosphate (UDP)-sugars and its role in bone formation is unknown. We confirmed P2Y₁₄ expression in primary murine osteoblasts (CB-Ob) and the C2C12-BMP2 osteoblastic cell line (C2-Ob). UDP-glucose (UDPG) had undiscernible effects on cAMP levels, however, induced dose-dependent elevations in the cytosolic free calcium concentration ([Ca²⁺]_i) in CB-Ob, but not C2-Ob cells. To antagonize the P2Y₁₄ function, we used the P2Y₁₄ inhibitor PPTN or generated CRISPR-Cas9-mediated P2Y₁₄ knockout C2-Ob clones (Y14_KO). P2Y₁₄ inhibition facilitated calcium signalling and altered basal cAMP levels in both models of osteoblasts. Importantly, P2Y₁₄ inhibition augmented Ca²⁺ signalling in response to ATP, ADP and mechanical stimulation. P2Y₁₄ knockout or inhibition reduced osteoblast proliferation and decreased ERK1/2 phosphorylation and increased AMPKα phosphorylation. During in vitro osteogenic differentiation, P2Y₁₄ inhibition modulated the timing of osteogenic gene expression, collagen deposition, and mineralization, but did not significantly affect differentiation status by day 28. Of interest, while P2ry14^-/- mice from the International Mouse Phenotyping Consortium were similar to wild-type controls in bone mineral density, their tibia length was significantly increased. We conclude that P2Y₁₄ in osteoblasts reduces cell responsiveness to mechanical stimulation and mechanotransductive signalling and modulates osteoblast differentiation.

Bone Tissue Engineering in the Growing Calvaria Using Dipyridamole-Coated, Three-Dimensionally-Printed Bioceramic Scaffolds: Construct Optimization and Effects on Cranial Suture Patency

BACKGROUND

Three-dimensionally-printed bioceramic scaffolds composed of β-tricalcium phosphate delivering the osteogenic agent dipyridamole can heal critically sized calvarial defects in skeletally mature translational models. However, this construct has yet to be applied to growing craniofacial models. In this study, the authors implanted three-dimensionally-printed bioceramic/dipyridamole scaffolds in a growing calvaria animal model and evaluated bone growth as a function of geometric scaffold design and dipyridamole concentration. Potential adverse effects on the growing suture were also evaluated.

METHODS

Bilateral calvarial defects (10 mm) were created in 5-week-old (approximately 1.1 kg) New Zealand White rabbits (n = 16 analyzed). Three-dimensionally-printed bioceramic scaffolds were constructed in quadrant form composed of varying pore dimensions (220, 330, and 500 μm). Each scaffold was coated with collagen and soaked in varying concentrations of dipyridamole (100, 1000, and 10,000 μM). Controls consisted of empty defects. Animals were killed 8 weeks postoperatively. Calvariae were analyzed using micro-computed tomography, three-dimensional reconstruction, and nondecalcified histologic sectioning.

RESULTS

Scaffold-induced bone growth was statistically greater than bone growth in empty defects (p = 0.02). Large scaffold pores, 500 μm, coated in 1000 μM dipyridamole yielded the most bone growth and lowest degree of scaffold presence within the defect. Histology showed vascularized woven and lamellar bone along with initial formation of vascular canals within the scaffold lattice. Micro-computed tomographic and histologic analysis revealed patent calvarial sutures without evidence of ectopic bone formation across all dipyridamole concentrations.

CONCLUSION

The authors present an effective pediatric bone tissue-engineering scaffold design and dipyridamole concentration that is effective in augmentation of calvarial bone generation while preserving cranial suture patency.

Signaling of the Purinergic System in the Joint

The joint is a complex anatomical structure consisting of different tissues, each with a particular feature, playing together to give mobility and stability at the body. All the joints have a similar composition including cartilage for reducing the friction of the movement and protecting the underlying bone, a synovial membrane that produces synovial fluid to lubricate the joint, ligaments to limit joint movement, and tendons for the interaction with muscles. Direct or indirect damage of one or more of the tissues forming the joint is the foundation of different pathological conditions. Many molecular mechanisms are involved in maintaining the joint homeostasis as well as in triggering disease development. The molecular pathway activated by the purinergic system is one of them.The purinergic signaling defines a group of receptors and intermembrane channels activated by adenosine, adenosine diphosphate, adenosine 5’-triphosphate, uridine triphosphate, and uridine diphosphate. It has been largely described as a modulator of many physiological and pathological conditions including rheumatic diseases. Here we will give an overview of the purinergic system in the joint describing its expression and function in the synovium, cartilage, ligament, tendon, and bone with a therapeutic perspective.

Effect of clopidogrel in bone healing-experimental study in rabbits

BACKGROUND

Clopidogrel is a widely prescribed drug for prevention of myocardial infarction and stroke in patients at risk. It inhibits thrombus formation via inhibition of the P2Y12 purinergic receptor on platelets, which is important in their activation by ADP. However, the P2Y12 receptor has also been found to be expressed in both osteoblasts and osteoclasts. Accumulated evidence suggests that purinergic receptors regulate important functions of bone turnover. Previous studies on the effect of clopidogrel on bone metabolism indicated potential harmful effects, but their results remain conflicting. Thus, clopidogrel treatment may affect bone healing, but it has not yet been studied.

AIM

To evaluate if continuous perioperative clopidogrel treatment has any negative effect on bone healing in the rabbit calvarial defect model.

METHODS

Sixteen male white New Zealand rabbits were randomly assigned in two groups: One group received daily 3 mg/kg of clopidogrel per os and the other group received the vehicle alone for a week prior to the surgical procedures; the treatments were continued for another 6 wk postoperatively. The surgical procedures included generation of two circular calvarial defects 11 mm in diameter in every animal. After the 6-wk period of healing, postmortem radiographic and histomorphometric evaluation of the defects was performed.

RESULTS

Both the surgical procedures and the postoperative period were uneventful and well tolerated by all the animals, without any surgical wound dehiscence, signs of infection or other complication. New bone was formed either inwards from the defect margins or in the central portion of the defect as separated bony islets. While defect healing was still incomplete in both groups, the clopidogrel group had significantly improved radiographic healing scores. Moreover, the histomorphometric analysis showed that bone regeneration (%) was 28.07 ± 7.7 for the clopidogrel group and 19.47 ± 4.9 for the control group, showing a statistically significant difference between them (P = 0.018). Statistically significant difference was also found in the defect bridging (%), i.e. 72.17 ± 21.2 for the clopidogrel group and 41.17 ± 8.5 for the control group, respectively (P = 0.004), whereas there was no statistical difference in bone tissue density between the groups.

CONCLUSION

Our results indicate that maintenance of perioperative clopidogrel treatment does not negatively affect bone healing but rather promotes it. Further research is needed in order to find useful applications of this finding.

Dipyridamole-loaded 3D-printed bioceramic scaffolds stimulate pediatric bone regeneration in vivo without disruption of craniofacial growth through facial maturity

This study investigates a comprehensive model of bone regeneration capacity of dypiridamole-loaded 3D-printed bioceramic (DIPY-3DPBC) scaffolds composed of 100% beta-tricalcium phosphate (β -TCP) in an immature rabbit model through the time of facial maturity. The efficacy of this construct was compared to autologous bone graft, the clinical standard of care in pediatric craniofacial reconstruction, with attention paid to volume of regenerated bone by 3D reconstruction, histologic and mechanical properties of regenerated bone, and long-term safety regarding potential craniofacial growth restriction. Additionally, long-term degradation of scaffold constructs was evaluated. At 24 weeks in vivo, DIPY-3DPBC scaffolds demonstrated volumetrically significant osteogenic regeneration of calvarial and alveolar defects comparable to autogenous bone graft with favorable biodegradation of the bioactive ceramic component in vivo. Characterization of regenerated bone reveals osteogenesis of organized, vascularized bone with histologic and mechanical characteristics comparable to native bone. Radiographic and histologic analyses were consistent with patent craniofacial sutures. Lastly, through application of 3D morphometric facial surface analysis, our results support that DIPY-3DPBC scaffolds do not cause premature closure of sutures and preserve normal craniofacial growth. Based on this novel evaluation model, this DIPY-3DPBC scaffold strategy is a promising candidate as a safe, efficacious pediatric bone tissue engineering strategy.

Repair of Critical-Sized Long Bone Defects Using Dipyridamole-Augmented 3D-Printed Bioactive Ceramic Scaffolds

There are over two million long bone defects treated in the United States annually, of which ~5% will not heal without significant surgical intervention. While autogenous grafting is the standard of care in simple defects, a customized scaffold for large defects in unlimited quantities is not available. Recently, a three-dimensionally (3D)-printed bioactive ceramic (3DPBC) scaffold has been successfully utilized in the of repair critical-sized (CSD) long bone defects in vivo. In this study, 3DPBC scaffolds were augmented with dipyridamole (DIPY), an adenosine A2A receptor (A_2A R) indirect agonist, because of its known effect to enhance bone formation. CSD full thickness segmental defects (~11 mm × full thickness) defects were created in the radial diaphysis in New Zealand white rabbits (n = 24). A customized 3DPBC scaffold composed of β-tricalcium phosphate was placed into the defect site. Groups included scaffolds that were collagen-coated (COLL), or immersed in 10, 100, or 1,000 μM DIPY solution. Animals were euthanized 8 weeks post-operatively and the radii/ulna-scaffold complex retrieved en bloc, for micro-CT, histological, and mechanical analysis. Bone growth was assessed exclusively within scaffold pores and evaluated by microCT and advanced reconstruction software. Biomechanical properties were evaluated utilizing nanoindentation to assess the newly regenerated bone for elastic modulus (E) and hardness (H). MicroCT reconstructions illustrated bone in-growth throughout the scaffold, with an increase in bone volume dependent on the DIPY dosage. The histological evaluation did not indicate any adverse immune response while revealing progressive remodeling of bone. These customized biologic 3DPBC scaffolds have the potential of repairing and regenerating bone. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2499-2507, 2019.

Regeneration of a Pediatric Alveolar Cleft Model Using Three-Dimensionally Printed Bioceramic Scaffolds and Osteogenic Agents: Comparison of Dipyridamole and rhBMP-2

BACKGROUND

Alveolar clefts are traditionally treated with secondary bone grafting, but this is associated with morbidity and graft resorption. Although recombinant human bone morphogenetic protein-2 (rhBMP-2) is under investigation for alveolar cleft repair, safety concerns remain. Dipyridamole is an adenosine receptor indirect agonist with known osteogenic potential. This study compared dipyridamole to rhBMP-2 at alveolar cleft defects delivered using bioceramic scaffolds.

METHODS

Skeletally immature New Zealand White rabbits underwent unilateral, 3.5 × 3.5-mm alveolar resection adjacent to the growing suture. Five served as negative controls. The remaining defects were reconstructed with three-dimensionally printed bioceramic scaffolds coated with 1000 μm of dipyridamole (n = 6), 10,000 μm of dipyridamole (n = 7), or 0.2 mg/ml of rhBMP-2 (n = 5). At 8 weeks, new bone was quantified. Nondecalcified histologic evaluation was performed, and new bone was evaluated mechanically. Statistical analysis was performed using a generalized linear mixed model and the Wilcoxon rank sum test.

RESULTS

Negative controls did not heal, whereas new bone formation bridged all three-dimensionally printed bioceramic treatment groups. The 1000-μm dipyridamole scaffolds regenerated 28.03 ± 7.38 percent, 10,000-μm dipyridamole scaffolds regenerated 36.18 ± 6.83 percent (1000 μm versus 10,000 μm dipyridamole; p = 0.104), and rhBMP-2-coated scaffolds regenerated 37.17 ± 16.69 percent bone (p = 0.124 versus 1000 μm dipyridamole, and p = 0.938 versus 10,000 μm dipyridamole). On histology/electron microscopy, no changes in suture biology were evident for dipyridamole, whereas rhBMP-2 demonstrated early signs of suture fusion. Healing was highly cellular and vascularized across all groups. No statistical differences in mechanical properties were observed between either dipyridamole or rhBMP-2 compared with native bone.

CONCLUSION

Dipyridamole generates new bone without osteolysis and early suture fusion associated with rhBMP-2 in skeletally immature bone defects.

Dysregulation of ectonucleotidase-mediated extracellular adenosine during postmenopausal bone loss

Adenosine and its receptors play a key role in bone homeostasis and regeneration. Extracellular adenosine is generated from CD39 and CD73 activity in the cell membrane, through conversion of adenosine triphosphate to adenosine monophosphate (AMP) and AMP to adenosine, respectively. Despite the relevance of CD39/CD73 to bone health, the roles of these enzymes in bona fide skeletal disorders remain unknown. We demonstrate that CD39/CD73 expression and extracellular adenosine levels in the bone marrow are substantially decreased in animals with osteoporotic bone loss. Knockdown of estrogen receptors ESR1 and ESR2 in primary osteoprogenitors and osteoclasts undergoing differentiation showed decreased coexpression of membrane-bound CD39 and CD73 and lower extracellular adenosine. Targeting the adenosine A2B receptor using an agonist attenuated bone loss in ovariectomized mice. Together, these findings suggest a pathological association of purine metabolism with estrogen deficiency and highlight the potential of A2B receptor as a target to treat osteoporosis.

Local delivery of adenosine receptor agonists to promote bone regeneration and defect healing

Adenosine receptor activation has been investigated as a potential therapeutic approach to heal bone. Bone has enhanced regenerative potential when influenced by either direct or indirect adenosine receptor agonism. As investigators continue to elucidate how adenosine influences bone cell homeostasis at the cellular and molecular levels, a small but growing body of literature has reported successful in vivo applications of adenosine delivery. This review summarizes the role adenosine receptor ligation plays in osteoblast and osteoclast biology and remodeling/regeneration. It also reports on all the modalities described in the literature at this point for delivery of adenosine through in vivo models for bone healing and regeneration.

Dipyridamole Augments Three-Dimensionally Printed Bioactive Ceramic Scaffolds to Regenerate Craniofacial Bone

BACKGROUND

Autologous bone grafts remain a standard of care for the reconstruction of large bony defects, but limitations persist. The authors explored the bone regenerative capacity of customized, three-dimensionally printed bioactive ceramic scaffolds with dipyridamole, an adenosine A2A receptor indirect agonist known to enhance bone formation.

METHODS

Critical-size bony defects (10-mm height, 10-mm length, full-thickness) were created at the mandibular rami of rabbits (n = 15). Defects were replaced by a custom-to-defect, three-dimensionally printed bioactive ceramic scaffold composed of β-tricalcium phosphate. Scaffolds were uncoated (control), collagen-coated, or immersed in 100 μM dipyridamole. At 8 weeks, animals were euthanized and the rami retrieved. Bone growth was assessed exclusively within scaffold pores, and evaluated by micro-computed tomography/advanced reconstruction software. Micro-computed tomographic quantification was calculated. Nondecalcified histology was performed. A general linear mixed model was performed to compare group means and 95 percent confidence intervals.

RESULTS

Qualitative analysis did not show an inflammatory response. The control and collagen groups (12.3 ± 8.3 percent and 6.9 ± 8.3 percent bone occupancy of free space, respectively) had less bone growth, whereas the most bone growth was in the dipyridamole group (26.9 ± 10.7 percent); the difference was statistically significant (dipyridamole versus control, p < 0.03; dipyridamole versus collagen, p < 0.01 ). There was significantly more residual scaffold material for the collagen group relative to the dipyridamole group (p < 0.015), whereas the control group presented intermediate values (nonsignificant relative to both collagen and dipyridamole). Highly cellular and vascularized intramembranous-like bone healing was observed in all groups.

CONCLUSION

Dipyridamole significantly increased the three-dimensionally printed bioactive ceramic scaffold's ability to regenerate bone in a thin bone defect environment.

[A novel calcium phosphate cement pre-loaded with chitosan and small molecule adenosine for repairing large cranial defects in rats]

OBJECTIVE

To evaluate the effect of a novel biomaterial in repairing large cranial defects in rats.

METHODS

Eighteen SD rats were used to establish rat modes of large cranial defect (8 mm in diameter). The rat models were randomized into 3 groups and the cranial defects were repaired using different scaffold materials, namely CPC paste prepared with distilled water (CPC control group), CPC paste mixed with 10% chitosan (CPC/CN group), or CPC paste with 10% chitosan and 300 mg adenosine (CPC/CN/AD group). The defects were examined 12 weeks after the surgery with X-ray, CT, HE staining and quantitative assessments.

RESULTS

X-ray showed that the defect was repaired in all the groups. The fracture line became obscure and the defects were almost fully repaired by regenerated bone tissues in CPC/CN/AD group, which was consistent with CT findings. In all the 3 groups, HE staining revealed the presence of new bones in the defects and new vessels in and around the new bones without inflammatory cells. The new bone area was significantly greater in CPC/CN/AD group than in CPC/CN group and CPC control group (P<0.05). The new vessel density was the highest in CPC/CN/AD group (P>0.05) but similar between CPC/CN group and CPC control group (P>0.05).

CONCLUSION

This novel calcium phosphate cement pre-loaded with chitosan and small molecule adenosine can better promote bone regeneration than calcium phosphate cement for repairing large bone defects to serve as a good replacement material for bone regeneration.

The role of 3D printing in treating craniomaxillofacial congenital anomalies

Craniomaxillofacial congenital anomalies comprise approximately one third of all congenital birth defects and include deformities such as alveolar clefts, craniosynostosis, and microtia. Current surgical treatments commonly require the use of autogenous graft material which are difficult to shape, limited in supply, associated with donor site morbidity and cannot grow with a maturing skeleton. Our group has demonstrated that 3D printed bio-ceramic scaffolds can generate vascularized bone within large, critical-sized defects (defects too large to heal spontaneously) of the craniomaxillofacial skeleton. Furthermore, these scaffolds are also able to function as a delivery vehicle for a new osteogenic agent with a well-established safety profile. The same 3D printers and imaging software platforms have been leveraged by our team to create sterilizable patient-specific intraoperative models for craniofacial reconstruction. For microtia repair, the current standard of care surgical guide is a two-dimensional drawing taken from the contralateral ear. Our laboratory has used 3D printers and open source software platforms to design personalized microtia surgical models. In this review, we report on the advancements in tissue engineering principles, digital imaging software platforms and 3D printing that have culminated in the application of this technology to repair large bone defects in skeletally immature transitional models and provide in-house manufactured, sterilizable patient-specific models for craniofacial reconstruction.

Ticagrelor - toward more efficient platelet inhibition and beyond

Novel antiplatelet drugs, including ticagrelor, are being successively introduced into the therapy of atherothrombotic conditions due to their superiority over a standard combination of clopidogrel with acetylsalicylic acid in patients with acute coronary syndromes (ACS). A P2Y12 receptor antagonist, ticagrelor, is unique among antiplatelet drugs, because ticagrelor inhibits the platelet P2Y12 receptor in a reversible manner, and because it demonstrates a wide palette of advantageous pleiotropic effects associated with the increased concentration of adenosine. The pleiotropic effects of ticagrelor comprise cardioprotection, restoration of the myocardium after an ischemic event, promotion of the release of anticoagulative factors and, eventually, anti-inflammatory effects. Beyond the advantageous effects, the increased concentration of adenosine is responsible for some of ticagrelor's adverse effects, including dyspnea and bradycardia. Large-scale clinical trials demonstrated that both standard 12-month therapy and long-term use of ticagrelor reduce the risk of cardiovascular events in patients with ACS, but at the expense of a higher risk of major bleeding. Further trials focused on the use of ticagrelor in conditions other than ACS, including ischemic stroke, peripheral artery disease and status after coronary artery bypass grafting. The results of these trials suggest comparable efficacy and safety of ticagrelor and clopidogrel in extra-coronary indications, but firm conclusions are anticipated from currently ongoing studies. Here, we summarize current evidence on the superiority of ticagrelor over other P2Y12 antagonists in ACS, discuss the mechanism underlying the drug-drug interactions and pleiotropic effects of ticagrelor, and present future perspectives of non-coronary indications for ticagrelor.

Dipyridamole enhances osteogenesis of three-dimensionally printed bioactive ceramic scaffolds in calvarial defects

PURPOSE

The objective of this study was to test the osteogenic capacity of dipyridamole-loaded, three-dimensionally printed, bioactive ceramic (3DPBC) scaffolds using a translational, skeletally mature, large-animal calvarial defect model.

MATERIALS AND METHODS

Custom 3DPBC scaffolds designed to present lattice-based porosity only towards the dural surface were either coated with collagen (control) or coated with collagen and immersed in a 100 μM concentration dipyridamole (DIPY) solution. Sheep (n = 5) were subjected to 2 ipsilateral trephine-induced (11-mm diameter) calvarial defects. Either a control or a DIPY scaffold was placed in each defect, and the surgery was repeated on the contralateral side 3 weeks later. Following sacrifice, defects were evaluated through microcomputed tomography and histologic analysis for bone, scaffold, and soft tissue quantification throughout the defect. Parametric and non-parametric methods were used to determine statistical significance based on data distribution.

RESULTS

No exuberant or ectopic bone formation was observed, and no histologic evidence of inflammation was noted within the defects. Osteogenesis was higher in DIPY-coated scaffolds compared to controls at 3 weeks (p = 0.013) and 6 weeks (p = 0.046) in vivo. When bone formation was evaluated as a function of defect radius, average bone formation was higher for DIPY relative to control scaffolds at both time points (significant at defect central regions at 3 weeks and at margins at 6 weeks, p = 0.046 and p = 0.031, respectively).

CONCLUSION

Dipyridamole significantly improves the calvarial bone regeneration capacity of 3DPBC scaffolds. The most significant difference in bone regeneration was observed centrally within the interface between the 3DPBC scaffold and the dura mater.

Three dimensionally printed bioactive ceramic scaffold osseoconduction across critical-sized mandibular defects

BACKGROUND

Vascularized bone tissue transfer, commonly used to reconstruct large mandibular defects, is challenged by long operative times, extended hospital stay, donor-site morbidity, and resulting health care. 3D-printed osseoconductive tissue-engineered scaffolds may provide an alternative solution for reconstruction of significant mandibular defects. This pilot study presents a novel 3D-printed bioactive ceramic scaffold with osseoconductive properties to treat segmental mandibular defects in a rabbit model.

METHODS

Full-thickness mandibulectomy defects (12 mm) were created at the mandibular body of eight adult rabbits and replaced by 3D-printed ceramic scaffold made of 100% β-tricalcium phosphate, fit to defect based on computed tomography imaging. After 8 weeks, animals were euthanized, the mandibles were retrieved, and bone regeneration was assessed. Bone growth was qualitatively assessed with histology and backscatter scanning electron microscopy, quantified both histologically and with micro computed tomography and advanced 3D image reconstruction software, and compared to unoperated mandible sections (UMSs).

RESULTS

Histology quantified scaffold with newly formed bone area occupancy at 54.3 ± 11.7%, compared to UMS baseline bone area occupancy at 55.8 ± 4.4%, and bone area occupancy as a function of scaffold free space at 52.8 ± 13.9%. 3D volume occupancy quantified newly formed bone volume occupancy was 36.3 ± 5.9%, compared to UMS baseline bone volume occupancy at 33.4 ± 3.8%, and bone volume occupancy as a function of scaffold free space at 38.0 ± 15.4%.

CONCLUSIONS

3D-printed bioactive ceramic scaffolds can restore critical mandibular segmental defects to levels similar to native bone after 8 weeks in an adult rabbit, critical sized, mandibular defect model.

Ecto-5'-nucleotidase (CD73) regulates bone formation and remodeling during intramembranous bone repair in aging mice

Ecto-5'-nucleotidase (CD73) generates adenosine, an osteoblast activator and key regulator of skeletal growth. It is unknown, however, if CD73 regulates osteogenic differentiation during fracture healing in adulthood, and in particular how CD73 activity regulates intramembranous bone repair in the elderly. Monocortical tibial defects were created in 46-52-week-old wild type (WT) and CD73 knock-out mice (CD73-/-) mice. Injury repair was analyzed at post-operative days 5, 7, 14 and 21 by micro-computed tomography (micro-CT), histomorphometry, proliferating cell nuclear antigen (PCNA) immunostaining, alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) histochemistry. Middle-aged CD73 knock-out mice exhibited delayed bone regeneration and significantly reduced bone matrix deposition detected by histomorphometry and micro-CT. Cell proliferation, ALP activity and osteoclast number were reduced in the CD73-/- mice, suggesting a combined defect in bone formation and resorption due the absence of CD73 activity in this model of intramembranous bone repair. Results from this study demonstrate that osteoblast activation through CD73 activity is essential during bone repair in aging mice, and it may present a drugable target for future biomimetic therapeutic approaches that aim at enhancing bone formation in the elderly patients.

Netrins & Semaphorins: Novel regulators of the immune response

Netrins and semaphorins, members of the neuronal guidance cue family, exhibit a rich biology with significant roles that extend beyond chemotactic guidance of the axons to build the neuronal patterns of the body. Screening of adult tissues and specific cellular subsets have illuminated that these proteins are also abundantly expressed under both steady state and pathological scenarios. This observation suggests that, in addition to their role in the development of the axonal tree, these proteins possess additional novel functions in adult physiopathology. Notably, a series of striking evidence has emerged in the literature describing their roles as potent regulators of both innate and adaptive immunity, providing extra dimension to our knowledge of neuronal guidance cues. In this review, we summarize the key complex roles of netrins and semaphorins outside the central nervous system (CNS) with focus on their immunomodulatory functions that impact pathophysiological conditions.