The Embryonic Chick Femur Organotypic Model as a Tool to Analyze the Angiotensin II Axis on Bone Tissue

Integrative tissue, cellular and molecular responsiveness of an innovative ex vivo model of the Staphylococcus aureus-mediated bone infection

Osteomyelitis is a pathological condition of the bone, frequently associated with the presence of infectious agents - namely Staphylococcus aureus - that induce inflammation and tissue destruction. Recent advances in the understanding of its pathophysiology and the identification of innovative therapeutic approaches were gathered from experimental in vitro and in vivo systems. However, cell culture models offer limited representativeness of the cellular functionality and the cell-cell and cell-matrix interactions, further failing to mimic the three-dimensional tissue organization; and animal models allow for limited mechanistic assessment given the complex nature of systemic and paracrine regulatory systems and are endorsed with ethical constraints. Accordingly, this study aims at the establishment and assessment of a new ex vivo bone infection model, upon the organotypic culture of embryonic chicken femurs colonized with S. aureus, highlighting the model responsiveness at the molecular, cellular, and tissue levels. Upon infection with distinct bacterial inoculums, data reported an initial exponential bacterial growth, followed by diminished metabolic activity. At the tissue level, evidence of S. aureus-mediated tissue destruction was attained and demonstrated through distinct methodologies, conjoined with decreased osteoblastic/osteogenic and increased osteoclastic/osteoclastogenic functionalities-representative of the osteomyelitis clinical course. Overall, the establishment and characterization of an innovative bone tissue infection model that is simple, reproducible, easily manipulated, cost-effective, and simulates many features of human osteomyelitis, further allowing the maintenance of the bone tissue's three-dimensional morphology and cellular arrangement, was achieved. Model responsiveness was further demonstrated, showcasing the capability to improve the research pipeline in bone tissue infection-related research.

Ex Vivo Osteogenesis Induced by Calcium Silicate-Based Cement Extracts

Calcium silicate-based cements are used in a variety of clinical conditions affecting the pulp tissue, relying on their inductive effect on tissue mineralization. This work aimed to evaluate the biological response of calcium silicate-based cements with distinct properties-the fast-setting Biodentine™ and TotalFill^® BC RRM™ Fast Putty, and the classical slow-setting ProRoot^® MTA, in an ex vivo model of bone development. Briefly, eleven-day-old embryonic chick femurs were cultured for 10 days in organotypic conditions, being exposed to the set cements' eluates and, at the end of the culture period, evaluated for osteogenesis/bone formation by combining microtomographic analysis and histological histomorphometric assessment. ProRoot^® MTA and TotalFill^® extracts presented similar levels of calcium ions, although significantly lower than those released from Biodentine^TM. All extracts increased the osteogenesis/tissue mineralization, assayed by microtomographic (BV/TV) and histomorphometric (% of mineralized area; % of total collagen area, and % of mature collagen area) indexes, although displaying distinct dose-dependent patterns and quantitative values. The fast-setting cements displayed better performance than that of ProRoot^® MTA, with Biodentine^TM presenting the best performance, within the assayed experimental model.

Repurposing sarecycline for osteoinductive therapies: an in vitro and ex vivo assessment

INTRODUCTION

Tetracyclines (TCs) embrace a class of broad-spectrum antibiotics with unrelated effects at sub-antimicrobial levels, including an effective anti-inflammatory activity and stimulation of osteogenesis, allowing their repurposing for different clinical applications. Recently, sarecycline (SA)-a new-generation molecule with a narrower antimicrobial spectrum-was clinically approved due to its anti-inflammatory profile and reduced adverse effects verified with prolonged use. Notwithstanding, little is known about its osteogenic potential, previously verified for early generation TCs.

MATERIALS AND METHODS

Accordingly, the present study is focused on the assessment of the response of human bone marrow-derived mesenchymal stromal cells (hBMSCs) to a concentration range of SA, addressing the metabolic activity, morphology and osteoblastic differentiation capability, further detailing the modulation of Wnt, Hedgehog, and Notch signaling pathways. In addition, an ex vivo organotypic bone development system was established in the presence of SA and characterized by microtomographic and histochemical analysis.

RESULTS

hBMSCs cultured with SA presented a significantly increased metabolic activity compared to control, with an indistinguishable cell morphology. Moreover, RUNX2 expression was upregulated 2.5-fold, and ALP expression was increased around sevenfold in the presence of SA. Further, GLI2 expression was significantly upregulated, while HEY1 and HNF1A were downregulated, substantiating Hedgehog and Notch signaling pathways' modulation. The ex vivo model developed in the presence of SA presented a significantly enhanced collagen deposition, extended migration areas of osteogenesis, and an increased bone mineral content, substantiating an increased osteogenic development.

CONCLUSION

Summarizing, SA is a promising candidate for drug repurposing within therapies envisaging the enhancement of bone healing/regeneration.

Hydrothermal Synthesis of Fluorapatite Coatings over Titanium Implants for Enhanced Osseointegration-An In Vivo Study in the Rabbit

This work aims at the development and characterization of fluorapatite coatings, innovatively prepared by the hydrothermal method, aiming for enhanced osseointegration of titanium implants. Fluoride-containing coatings were prepared and characterized by scanning and transmission electron microscopy, Fourier-transform infrared spectroscopy-attenuated total reflectance, and X-ray photoelectron spectroscopy. The biological response was characterized by microtomographic evaluation and histomorphometric analysis upon orthotopic implantation in a translational rabbit experimental model. Physic-chemical analysis revealed the inclusion of fluoride in the apatite lattice with fluorapatite formation, associated with the presence of citrate species. The in vivo biological assessment of coated implants revealed an enhanced bone formation process-with increased bone-to-implant contact and bone volume. The attained enhancement of the osteogenic process may be attributable to the conjoined modulatory activity of selected fluoride and citrate levels within the produced coatings. In this regard, the production of fluorapatite coatings with citrate, through the hydrothermal method, entails a promising approach for enhanced osseointegration in implant dentistry and orthopedic applications.

From Blood to Bone-The Osteogenic Activity of L-PRF Membranes on the Ex Vivo Embryonic Chick Femur Development Model

(1) Background: To evaluate the effects of the direct and indirect contact of leukocyte and platelet-rich fibrin (L-PRF) on bone development, in an ex vivo embryonic chick femur model. (2) Methods: Both sections of L-PRF membranes (red and yellow portions) were evaluated with scanning electron microscopy and histochemical staining. The in vivo angiogenic activity was evaluated using a chorioallantoic membrane model. The osteogenic activity was assessed with an organotypic culture of embryonic chick femora through direct and indirect contact, and assessment was conducted by microtomographic and histological analysis. Descriptive statistics, One-Way ANOVA and Tukey’s multiple comparisons tests were performed for datasets that presented a normal distribution, and Kruskal-Wallis tests were performed for non-parametric datasets. A significance level of 0.05 was considered. (3) Results: The L-PRF induced angiogenesis reflected by a higher number and a larger and more complex gauge in the vessels that invaded the membrane. The physical presence of the membrane over the bone (direct contact) unleashes the full potential of the L-PRF effects on bone growth enhancement. The greatest increase in mineral content was observed in the diaphysis region. (4) Conclusion: The L-PRF direct contact group presented higher values on mineral content for bone volume, bone surface and bone mineral density than the indirect contact and control groups.