Immune response and innervation signatures in aseptic hip implant loosening.

BACKGROUND: Aseptic loosening (AL) of hip prosthesis presents inflammation and pain as sign and symptom similarly to arthritis pathologies. Still, the immune and innervation profiles in hip AL remain unclear and their interplay is poorly explored. Herein, local tissue inflammatory response, sensory and sympathetic innervation as well as associated local mediators were assessed in hip joint microenvironment underlying AL and compared to osteoarthritis (OA). METHODS: Histopathological analysis, immune cells (macrophages, T, B cells and PMNs) as well as sensory and sympathetic nerve fibers (SP(+), CGRP(+), TH(+)) distribution and profiles were analyzed on tissues retrieved from patients with failed hip prostheses due to AL (n = 20) and hip OA (n = 15) by immunohistochemistry. Additionally, transcriptional levels of pro-inflammatory cytokines (TNF-α, IL-1ß, IL-6, IL-12a, iNOS), anti-inflammatory cytokine (IL-10), osteoclastic factor (RANKL) and bone remodeling factor (TGF-ß1) were locally evaluated by qRT-PCR. Serum TGF-ß1 levels were assessed preoperatively by ELISA. RESULTS: Histopathological analysis revealed that tissues, aseptic interface membranes of AL patients had distinct tissue architecture and immune cells profile when compared to OA synovial tissues. Macrophages, T cells and B cells showed significant differences in tissue distribution. In OA, inflammation is mostly confined to the vicinity of synovial membrane while in AL macrophages infiltrated throughout the tissue. This differential immune profile is also accompanied with a distinct pattern of sensory and sympathetic innervation. Importantly, in AL patients, a lack of sympathetic innervation aseptic interface membranes without compensation mechanisms at cellular levels was observed with simultaneous reorganization of sensorial innervation. Despite the different histopathological portrait, AL and OA patients exhibited similar transcriptional levels of genes encoding key proteins in local immune response. Nevertheless, in both pathologies, TGF-ß1 expression was prominent in sites where the inflammation is occurring. However, at systemic level no differences were found. CONCLUSION: These findings indicate that AL patients exhibit different local inflammatory response and innervation signatures from OA patients in hip joint. These insights shed the light on neuro-immune interplay in AL and highlight the need to better understand this crosstalk to unravel potential mechanisms for targeted-therapies to improve hip joint lifetime and treatment.

The Effect of High Pressure on Polymorphs of a Derivative of Blatter's Radical: Identification of the Structural Signatures of Subtle Phase Transitions.

The effect of pressure on the α and ß polymorphs of a derivative of Blatter's radical, 3-phenyl-1-(pyrid-2-yl)-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl, has been investigated using single-crystal X-ray diffraction to maximum pressures of 5.76 and 7.42 GPa, respectively. The most compressible crystallographic direction in both structures lies parallel to π-stacking interactions, which semiempirical Pixel calculations indicate are also the strongest interactions present. The mechanism of compression in perpendicular directions is determined by void distributions. Discontinuities in the vibrational frequencies observed in Raman spectra measured between ambient pressure and ∼5.5 GPa show that both polymorphs undergo phase transitions, the α phase at 0.8 GPa and the ß phase at 2.1 GPa. The structural signatures of the transitions, which signal the onset of compression of initially more rigid intermolecular contacts, were identified from the trends in the occupied and unoccupied volumes of the unit cell with pressure and in the case of the ß phase by deviations from an ideal model of compression defined by Birch-Murnaghan equations of state.

Osteoclasts degrade fibrinogen scaffolds and induce mesenchymal stem/stromal osteogenic differentiation.

Fibrinogen (Fg) is a pro-inflammatory protein with pro-healing properties. Previous work showed that fibrinogen 3D scaffolds (Fg-3D) promote bone regeneration, but the cellular players were not identified. Osteoclasts are bone resorbing cells that promote bone remodeling in close crosstalk with osteoblasts. Herein, the capacity of osteoclasts differentiated on Fg-3D to degrade the scaffolds and promote osteoblast differentiation was evaluated in vitro. Fg-3D scaffolds were prepared by freeze-drying and osteoclasts were differentiated from primary human peripheral blood monocytes. Results obtained showed osteoclasts expressing the enzymes cathepsin K and tartrate resistant acid phosphatase colonizing Fg-3D scaffolds. Osteoclasts were able to significantly degrade Fg-3D, reducing the scaffold's area, and increasing D-dimer concentration, a Fg degradation product, in their culture media. Osteoclast conditioned media from the first week of differentiation promoted significantly stronger human primary mesenchymal stem/stromal cell (MSC) osteogenic differentiation, evaluated by alkaline phosphatase activity. Moreover, week 1 osteoclast conditioned media promoted earlier MSC osteogenic differentiation, than chemical osteogenesis inductors. TGF-ß1 was found increased in osteoclast conditioned media from week 1, when compared to week 3 of differentiation. Taken together, our results suggest that osteoclasts are able to differentiate and degrade Fg-3D, producing factors like TGF-ß1 that promote MSC osteogenic differentiation.

Chitosan porous 3D scaffolds embedded with resolvin D1 to improve in vivo bone healing.

The aim of this study was to investigate the effect chitosan (Ch) porous 3D scaffolds embedded with resolvin D1 (RvD1), an endogenous pro-resolving lipid mediator, on bone tissue healing. These scaffolds previous developed by us have demonstrated to have immunomodulatory properties namely in the modulation of the macrophage inflammatory phenotypic profile in an in vivo model of inflammation. Herein, results obtained in an in vivo rat femoral defect model demonstrated that two months after Ch + RvD1 scaffolds implantation, an increase in new bone formation, in bone trabecular thickness, and in collagen type I and Coll I/Coll III ratio were observed. These results suggest that Ch scaffolds embedded with RvD1 were able to lead to the formation of new bone with improvement of trabecular thickness. This study shows that the presence of RvD1 in the acute phase of the inflammatory response to the implanted biomaterial had a positive role in the subsequent bone tissue repair, thus demonstrating the importance of innovative approaches for the control of immune responses to biomedical implants in the design of advanced strategies for regenerative medicine. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1626-1633, 2018.

The two faces of metal ions: From implants rejection to tissue repair/regeneration.

The paradigm of metallic ions as exclusive toxic agents is changing. During the last 60 years, knowledge about toxicological and immunological reactions to metal particles and ions has advanced considerably. Hip prostheses, namely metal-on-metal bearings, have prompted studies about excessive and prolonged exposure to prosthetic debris. In that context, the interactions of metal particles and ions with cells and tissues are mostly harmful, inducing immune responses that lead to osteolysis and implant failure. However, in the last decade, new strategies to promote immunomodulation and healing have emerged based on the unique properties of metallic ions. The atom-size and charge enable ions to interact with key macromolecules (e.g. proteins, nucleic acids) that affect cellular function. Moreover, these agents are inexpensive, stable and can be integrated in biomaterials, which may open new avenues for a novel generation of medical devices. Herein, orthopedic devices are discussed as models for adverse responses to metal ions, and debated together with the potential to use metal ions-based therapies, thus bridging the gap between unmet clinical needs and cutting-edge research. In summary, this review addresses the two "faces" of metallic ions, from pathological responses to innovative research strategies that use metal ions for regenerative medicine.

Fracture pain-Traveling unknown pathways.

An increase of fracture incidence is expected for the next decades, mostly due to the undeniable increase of osteoporotic fractures, associated with the rapid population ageing. The rise in sports-related fractures affecting the young and active population also contributes to this increased fracture incidence, and further amplifies the economical burden of fractures. Fracture often results in severe pain, which is a primary symptom to be treated, not only to guarantee individual's wellbeing, but also because an efficient management of fracture pain is mandatory to ensure proper bone healing. Here, we review the available data on bone innervation and its response to fracture, and discuss putative mechanisms of fracture pain signaling. In addition, the common therapeutic approaches to treat fracture pain are discussed. Although there is still much to learn, research in fracture pain has allowed an initial insight into the mechanisms involved. During the inflammatory response to fracture, several mediators are released and will putatively activate and sensitize primary sensory neurons, in parallel, intense nerve sprouting that occurs in the fracture callus area is also suggested to be involved in pain signaling. The establishment of hyperalgesia and allodynia after fracture indicates the development of peripheral and central sensitization, still, the underlying mechanisms are largely unknown. A major concern during the treatment of fracture pain needs to be the preservation of proper bone healing. However, the most common therapeutic agents, NSAIDS and opiates, can cause significant side effects that include fracture repair impairment. The understanding of the mechanisms of fracture pain signaling will allow the development of mechanisms-based therapies to effectively and safely manage fracture pain.

Bone Injury and Repair Trigger Central and Peripheral NPY Neuronal Pathways.

Bone repair is a specialized type of wound repair controlled by complex multi-factorial events. The nervous system is recognized as one of the key regulators of bone mass, thereby suggesting a role for neuronal pathways in bone homeostasis. However, in the context of bone injury and repair, little is known on the interplay between the nervous system and bone. Here, we addressed the neuropeptide Y (NPY) neuronal arm during the initial stages of bone repair encompassing the inflammatory response and ossification phases in femoral-defect mouse model. Spatial and temporal analysis of transcriptional and protein levels of NPY and its receptors, Y1R and Y2R, reported to be involved in bone homeostasis, was performed in bone, dorsal root ganglia (DRG) and hypothalamus after femoral injury. The results showed that NPY system activity is increased in a time- and space-dependent manner during bone repair. Y1R expression was trigged in both bone and DRG throughout the inflammatory phase, while a Y2R response was restricted to the hypothalamus and at a later stage, during the ossification step. Our results provide new insights into the involvement of NPY neuronal pathways in bone repair.

Fibrinogen scaffolds with immunomodulatory properties promote in vivo bone regeneration.

The hypothesis behind this work is that fibrinogen (Fg), classically considered a pro-inflammatory protein, can promote bone repair/regeneration. Injury and biomaterial implantation naturally lead to an inflammatory response, which should be under control, but not necessarily minimized. Herein, porous scaffolds entirely constituted of Fg (Fg-3D) were implanted in a femoral rat bone defect and investigated at two important time points, addressing the bone regenerative process and the local and systemic immune responses, both crucial to elucidate the mechanisms of tissue remodelling. Fg-3D led to early infiltration of granulation tissue (6 days post-implantation), followed by bone defect closure, including periosteum repair (8 weeks post-injury). In the acute inflammatory phase (6 days) local gene expression analysis revealed significant increases of pro-inflammatory cytokines IL-6 and IL-8, when compared with non-operated animals. This correlated with modified proportions of systemic immune cell populations, namely increased T cells and decreased B, NK and NKT lymphocytes and myeloid cell, including the Mac-1+ (CD18+/CD11b+) subpopulation. At 8 weeks, Fg-3D led to decreased plasma levels of IL-1ß and increased TGF-ß1. Thus, our data supports the hypothesis, establishing a link between bone repair induced by Fg-3D and the immune response. In this sense, Fg-3D scaffolds may be considered immunomodulatory biomaterials.

Role of protein environment and bioactive polymer grafting in the S. epidermidis response to titanium alloy for biomedical applications.

Joint implant-related infections, namely by Staphylococci, are a worldwide problem, whose consequences are dramatic. Various methods are studied to fight against these infections. Here, the proposed solution consists in grafting a bioactive polymer on joint implant surfaces in order to allow the control of the interactions with the living system. In this study, sodium styrene sulfonate, bearing sulfonate groups, was grafted on the surface of titanium alloys. Scanning Electron Microscopy, colorimetric method, Fourier-transformed infrared spectroscopy and contact angle measurements were applied to characterize the surfaces. Bacterial adhesion studies were studied on poly(sodium styrene sulfonate) grafted Ti6Al4V and Ti6Al4V surfaces previously adsorbed by proteins involved in the bacteria adhesion process. Fibrinogen and fibronectin were demonstrated to increase staphylococcal adhesion on Ti6Al4V surfaces. Ti6Al4V grafted sodium styrene sulfonate surfaces inhibited the adhesion of Staphylococcus epidermidis in 37% and 13% on pre-adsorbed surfaces with fibrinogen and fibronectin, respectively. The mechanism of the observed inhibiting bacteria adhesion properties is related to the differences of proteic conformations induced by poly(sodium styrene sulfonate) grafting.