Effect of cyclic mechanical stretch and titanium particles on prostaglandin E2 production by human macrophages in vitro

Mechanical and Immunological Regulation in Wound Healing and Skin Reconstruction

In the past decade, a new frontier in scarless wound healing has arisen because of significant advances in the field of wound healing realised by incorporating emerging concepts from mechanobiology and immunology. The complete integumentary organ system (IOS) regeneration and scarless wound healing mechanism, which occurs in specific species, body sites and developmental stages, clearly shows that mechanical stress signals and immune responses play important roles in determining the wound healing mode. Advances in tissue engineering technology have led to the production of novel human skin equivalents and organoids that reproduce cell–cell interactions with tissue-scale tensional homeostasis, and enable us to evaluate skin tissue morphology, functionality, drug response and wound healing. This breakthrough in tissue engineering has the potential to accelerate the understanding of wound healing control mechanisms through complex mechanobiological and immunological interactions. In this review, we present an overview of recent studies of biomechanical and immunological wound healing and tissue remodelling mechanisms through comparisons of species- and developmental stage-dependent wound healing mechanisms. We also discuss the possibility of elucidating the control mechanism of wound healing involving mechanobiological and immunological interaction by using next-generation human skin equivalents.

Mechano-Immunomodulation: Mechanoresponsive Changes in Macrophage Activity and Polarization

In recent years, biomaterial- and scaffold-based immunomodulation strategies were implemented in tissue regeneration efforts for manipulating macrophage polarization (a.k.a. phenotype or lineage commitment, or differentiation). Yet, most of our understanding of macrophage phenotype commitment and phagocytic capacity is limited to how physical cues (extracellular matrix stiffness, roughness, and topography) and soluble chemical cues (cytokines and chemokines released from the scaffold) influence macrophage polarization. In the context of immune response-tissue interaction, the mechanical cues experienced by the residing cells within the tissue also play a critical role in macrophage polarization and inflammatory response. However, there is no compiled study discussing the effect of the dynamic mechanical environment around the tissues on macrophage polarization and the innate immune response. The aim of this comprehensive review paper is 2-fold; (a) to highlight the importance of mechanical cues on macrophage lineage commitment and function and (b) to summarize the important studies dedicated to understand how macrophage polarization changes with different mechanical loading modalities. For the first time, this review paper compiles and compartmentalizes the studies investigating the role of dynamic mechanical loading with various modalities, amplitude, and frequency on macrophage differentiation. A deeper understanding of macrophage phenotype in mechanically dominant tissues (i.e. musculoskeletal tissues, lung tissues, and cardiovascular tissues) provides mechanistic insights into the design of mechano-immunomodulatory tissue scaffold for tissue regeneration.

Mechanical regulation of macrophage function - cyclic tensile force inhibits NLRP3 inflammasome-dependent IL-1β secretion in murine macrophages

Mechanical stress maintains tissue homeostasis by regulating many cellular functions including cell proliferation, differentiation, and inflammation and immune responses. In inflammatory microenvironments, macrophages in mechanosensitive tissues receive mechanical signals that regulate various cellular functions and inflammatory responses. Macrophage function is affected by several types of mechanical stress, but the mechanisms by which mechanical signals influence macrophage function in inflammation, such as the regulation of interleukin-1β by inflammasomes, remain unclear. In this review, we describe the role of mechanical stress in macrophage and monocyte cell function.

In Vitro Effect of 3D Plates Used for Surgical Treatment of Condylar Fractures on Prostaglandin E₂ (PGE₂) and Thromboxane B₂ (TXB₂) Concentration in THP-1 Macrophages

Recent studies have shown promising results concerning the effectiveness of 3D plates in terms of stabilization of condylar fractures. Despite the use of new techniques and new materials, we can still observe certain side effects, including the immune reaction of the body, which may lead to the excessive inflammation. The aim of this paper was to determine how the production of prostaglandin E₂ (PGE₂) and thromboxane B₂ (TXB₂) in THP-1 monocytes/macrophages is influenced by the titanium 3D plates and dedicated screws. The experiments were conducted on THP-1 monocytic cell line and macrophages derived from a THP-1cells. The concentrations of PGE₂ and TXB₂ released were measured by using immunoassay kit. Verification of plate-induced activation of THP-1 monocytes and macrophages and initiation of inflammatory reaction was conducted by flow cytometry. Despite some differences in the content of the implant devices our results showed that these plates did not statistically significantly increase the production of these prostanoids. Osteosynthesis of condylar fractures using 3D titanium mini-plates seems to be a good alternative to traditional plates due to their lack of stimulating the cyclooxygenase-dependent production of prostanoids; limiting the development of inflammatory reactions.

Protective effects of COX-2 inhibitor on titanium-particle-induced inflammatory osteolysis via the down-regulation of RANK/RANKL

Particle-wear-induced inflammatory osteolysis remains a major problem for the long-term success of total joint arthroplasty. Previous studies have demonstrated that cyclooxygenase-2 (COX-2) is expressed abundantly in the tissue around a failed implant. However, the role of COX-2 in the development of particle-wear-induced osteoclastogenesis remains unclear. The aim of the study was to test the hypothesis that Dynastat, a COX-2 inhibitor, ameliorates particle-wear-induced inflammatory osteoclastogenesis through the down-regulation of the receptor activators of nuclear factor-κB (RANK) and nuclear factor-κB ligand (RANKL) expression in a murine osteolysis model. Titanium (Ti) particles were introduced into established air pouches in BALB/c mice, followed by the implantation of calvaria bone from syngeneic littermates. Dynastat was given to mice intraperitoneally 2 days before the introduction of Ti particles and maintained until the mice were sacrificed. Pouch tissues were collected 14 days after Ti inoculation for molecular and histological analysis. The results showed that Dynastat has more impact on Ti-particle-induced prostaglandin E(2) expression and less on the expression of interleukin-1β and tumor necrosis factor-α. Dynastat inhibited Ti-particle-induced osteoclastogenesis by reducing the gene activation of RANK and RANKL, and diminishing the RANKL expression in Ti-particle-charged pouches. Dynastat markedly reduced the number of tartrate-resistant acid-phosphatase-positive cells in pouch tissues stimulated by Ti particles. In conclusion, this study provides evidence that Dynastat can markedly inhibit Ti-particle-induced osteoclastogenesis by the down-regulation of RANK/RANKL in a murine air pouch model, and is a promising therapeutic candidate for the treatment of inflammatory osteolysis induced by wear particles.

TGF-ß1 and FAK regulate periostin expression in PDL fibroblasts

Recently identified as a key component of the murine periodontal ligament (PDL), periostin has been implicated in the regulation of collagen fibrillogenesis and fibroblast differentiation. We investigated whether periostin protein is expressed in the human PDL in situ and the mechanisms regulating periostin expression in PDL fibroblasts in vitro. With immunohistochemistry, periostin protein was identified in the PDL, with expression lower in teeth with reduced occlusal loading. In vitro application of uniaxial cyclic strain to PDL fibroblasts elevated periostin mRNA levels, depending on the age of the patient. Treatment with transforming growth factor-beta1 (TGF-β1) also significantly increased periostin mRNA levels, an effect attenuated by focal adhesion kinase (FAK) inhibition. FAK-null fibroblasts contained no detectable periostin mRNA, even after stimulation with cyclic strain. In conclusion, periostin protein is strongly expressed in the human PDL. In vitro, periostin mRNA levels are modulated by cyclic strain as well as TGF-β1 via FAK-dependent pathways.

PGE2 signaling through the EP4 receptor on fibroblasts upregulates RANKL and stimulates osteolysis

Periprosthetic osteolysis is the most common cause of aseptic loosening in total joint arthroplasty. The role of inflammatory mediators such as prostaglandin E2 (PGE2) and osteoclast promoting factors including RANKL in the pathogenesis of osteolysis has been well characterized. However, the PGE2 receptor (EP1, EP2, or EP4), and cell type in which it is expressed, which is responsible for PGE2 induction of RANKL during wear debris-induced osteolysis, has yet to be elucidated. To address this, we used mice genetically deficient in these EP receptors to assess PGE2 and wear debris responses in vitro and in vivo. Wear debris-induced osteolysis and RANKL expression were observed at similar levels in WT, EP1(-/-), and EP2(-/-) mice, indicating that these receptors do not mediate PGE2 signals in this process. A conditional knockout approach was used to eliminate EP4 expression in FSP1(+) fibroblasts that are the predominant source of RANKL. In the absence of EP4, fibroblasts do not express RANKL after stimulation with particles or PGE2, nor do they exhibit high levels of osteoclasts and osteolysis. These results show that periprosthetic fibroblasts are important mediators of osteolysis through the expression of RANKL, which is induced after PGE2 signaling through the EP4 receptor.

Effect of etidronate on COX-2 expression and PGE(2) production in macrophage-like RAW 264.7 cells stimulated by titanium particles

BACKGROUND

The most common failure of total joint replacement is aseptic loosening in association with osteolysis. Previous reports have shown that prostaglandin E(2) (PGE(2)) secreted from macrophages that phagocytosed wear debris induced periprosthetic osteolysis. Many clinical studies have reported that bisphosphonate therapy reduced periprosthetic bone loss and loosening of the implants after total joint replacements. Bisphosphonates are synthetic compounds with the ability to decrease bone resorption. In addition, some bisphosphonates have been reported to have anti-inflammatory effects by reducing the secretion of pro-inflammatory cytokines. However, the mechanism of bisphosphonates that reduces periprosthetic bone resorption remains unclear. The purpose of this study was to investigate one of the mechanisms by which etidronate (EHDP) inhibits periprosthetic bone resorption.

METHODS

Macrophage-like RAW 264.7 cells were treated with EHDP at concentrations of 0.001, 0.01, 0.1, 1, 10, and 100 microM together with the titanium particles at a concentration of 1 mg/ml. After a 24-h culture period, total mRNA was isolated and reverse transcription-polymerase chain reaction (RT-PCR) was done to examine the expression of cyclooxygenase-2 (COX-2). The supernatants were also collected and production of PGE(2), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) were quantified using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Analyses showed that COX-2 expression and PGE(2) production were suppressed by EHDP in a dose-dependent manner. By 100 microM of EHDP, PGE(2) production of the cells was suppressed approximately to the level of the nonstimulated cells. Production of IL-1beta, IL-6, and TNF-alpha in the supernatant was also suppressed by EHDP.

CONCLUSIONS

The blockage effect of pro-inflammatory cytokines is a possible etidronate mechanism that reduces bone resorption around implants.

Upregulation of LITAF mRNA expression upon exposure to TiAlV and polyethylene wear particles in THP-1 macrophages

Tumor necrosis factor alpha (TNFalpha) plays a fundamental role in the pathogenesis of wear particle-induced periprosthetic osteolysis. However, particle-induced mechanisms that control TNFalpha gene expression are not yet well characterized. LITAF [lipopolysaccharide (LPS)-induced TNFalpha factor] is a novel transcription factor that regulates expression of the TNFalpha gene, but nothing is known about its role in wear particle-induced osteolysis. We evaluated the effect of titanium aluminum vanadium (TiAlV) and polyethylene particles on mRNA expression of LITAF. A human monocytic leukemia cell line (THP-1) was used in this in vitro study. THP-1 monocytes were differentiated to macrophage-like cells and exposed to LPS-detoxified polyethylene particles and prosthesis-derived TiAlV particles. Supernatant was used for TNFalpha protein measurement and total RNA was extracted from cells. LITAF was analyzed at the mRNA level using semiquantitative RT-PCR. Both polyethylene and TiAlV particles induced significant upregulation of LITAF mRNA that was followed by a significant TNFalpha response. These effects were dependent on the particle dose. Low particle concentrations exhibited no significant effect on expression of TNFalpha and LITAF mRNA. In comparison to exposure to polyethylene and TiAlV particles, LPS stimulation exhibited similar upregulation of LITAF mRNA, but led to an overwhelming TNFalpha response. Our findings provide evidence that LITAF is implicated in the pathogenesis of wear particle-induced osteolysis.

Substance P augments PGE2 and IL-6 production in titanium particles-stimulated fibroblasts from hip periprosthetic membrane

Aseptic loosening remains the primary cause of failure in total joint arthroplasty. Implant-derived particles are thought to be a main cause of osteolysis that leads to failure of total joint arthroplasty. The nervous system has been implicated in the etiology and pathogenesis of joint diseases. Substance P (SP) immunoreactive nerve fibers have been detected in the pseudomembrane and pseudocapsular tissues of aseptic loose hip prostheses, suggesting that SP might be involved in the process of aseptic loosening. Fibroblasts are abundant in periprosthetic membrane. Neuropeptides are able to modulate cytokine production by fibroblasts. In this study, we isolated fibroblasts from periprosthetic membrane at the time of revision hip arthroplasty performed because of aseptic loosening. Fibroblasts were stimulated with titanium (Ti) particles or SP. Prostaglandin (PG) E2 and interleukin-6 (IL-6) assays were performed using enzyme-linked immunosorbent assay kit. PGE2 and IL-6 secretion by fibroblasts have been significantly increased in the presence of Ti particles or SP. Moreover SP caused significant increase in PGE2 and IL-6 production by Ti particles-stimulated fibroblasts. Thus, SP and Ti particles acted synergistically to increase PGE2 and IL-6 secretion in fibroblasts from periprosthetic membrane.

Differential effects of uniaxial and biaxial strain on U937 macrophage-like cell morphology: Influence of extracellular matrix type proteins

Tissue engineering concepts have expanded in the last decade to consider the importance of biochemical signaling from extracellular matrix (ECM) proteins adhered to substrates such as polymeric and ceramic scaffolds. This study investigated combined ECM/mechanical factors on the key signaling cells (macrophages) for wound healing, since previously, mechanical strain and ECM proteins have only been considered separately for their effects on macrophage morphology. Human U937 macrophage-like cells were cultured on a model elastomeric membrane, coated with either collagen type I or poly-RGD peptide (ProNectin). The cells were subjected to cyclic uniform uniaxial or nonuniform biaxial strain with the Flexercell Tension Plus system to simulate strains that various soft tissue implants may undergo during the critical tissue-implant integration period. The surface coatings affected total cellular protein, which was significantly higher in cells on collagen than ProNectin coated surfaces after biaxial, but not uniaxial strain, whereas ProNectin coated surfaces caused a decrease in DNA following uniaxial, but not biaxial strain. Adding the protein coatings that relate to the wound healing process during tissue regeneration, elicited effects specific to the strain type imposed. The combination of these parameters caused changes in U937 macrophage-like cells that should be considered in the outcome of the desired performance in the tissue-material constructs.

Synergistic effects of mixed TiAlV and polyethylene wear particles on TNFα response in THP-1 macrophages / Synergistische Effekte gemischter TiAlV- und Polyethylen-Abriebpartikel auf die TNFα-Antwort in THP-1 Makrophagen

TNFalpha is a potent osteoclastogenic cytokine that has a fundamental role in the pathogenesis of wear particle-induced osteolysis. Wear particles of one composition and their biological effects are well characterised. In contrast, little is known about the effects of mixed particles with respect to mix ratio and particle concentration. We evaluated the effects of different mix ratios of polyethylene and TiAlV particles on TNFalpha response. We used a human monocytic cell line (THP-1) in this in vitro study. THP-1 monocytes were differentiated to macrophage-like cells and exposed to different mixtures of lipopolysaccharide-detoxified polyethylene and TiAlV particles. TNFalpha was analysed in culture supernatants using ELISAs. Both polyethylene and TiAlV particles induced a dose- and time-related release of TNFalpha, with maximum levels after 6 h. A PE/TiAlV mix ratio of 36:1 at 10(8) particles/ml induced significantly higher TNFalpha concentrations compared to equal particle concentrations of isolated TiAlV (p=0.047) or PE (p=0.044), indicating the synergistic effect of mixed particles. These results provide evidence that TiAlV and polyethylene particles have significant synergistic effects, depending on the mix ratio and particle concentrations. This supra-additive effect can contribute substantially to the pathogenesis of implant particle-induced osteolysis.

Abriebpartikel

The aseptic prosthetic loosening of hip and knee prosthesis is the most important cause of implant insufficiency. Bone loss as a result of the biological effect of wear particles is the main cause of such loosening. Wear particles develop their biological activity along different cellular pathways, above all via macrophages, foreign body giant cells as well as fibroblasts of the periprosthetic membrane. These cells induce particle-dependent bone resorption by means of proinflammatory cytokines, such as IL-1beta, TNF-alpha, IL-6 and PGE2. These factors induce the activation of osteoclasts as well as the suppression of osteoblasts. Neutrophil granulocytes and lymphocytes do not play an important role in the process of aseptic loosening. The different wear particles, such as ultra-high molecular weight polyethylene, metal particles, ceramic particles and polymethylmethacrylate can be morphologically recognized very easily. From the clinical point of view, the differentiation between acute or chronic implant infection and particle induced prosthetic loosening is very important, with the histomorphological differential diagnosis between septic and aseptic loosening and their combination being the key clinicopathological factor.

The central role of wear debris in periprosthetic osteolysis

Periprosthetic osteolysis remains the leading complication of total hip arthroplasty, often resulting in aseptic loosening of the implant, and a requirement for revision surgery. Wear-generated particular debris is the main cause of initiating this destructive process. The purpose of this article is to review recent advances in our understanding of how wear debris causes osteolysis, and emergent strategies for the avoidance and treatment of this disease. The most important cellular target for wear debris is the macrophage, which responds to particle challenge in two distinct ways, both of which contribute to increased bone resorption. First, it is well known that wear debris activates proinflammatory signaling, which leads to increased osteoclast recruitment and activation. More recently, it has been established that wear also inhibits the protective actions of antiosteoclastogenic cytokines such as interferon gamma, thus promoting differentiation of macrophages to bone-resorbing osteoclasts. Osteoblasts, fibroblasts, and possibly lymphocytes may also be involved in responses to wear. At a molecular level, wear particles activate MAP kinase cascades, NFkappaB and other transcription factors, and induce expression of suppressors of cytokine signaling. Strategies to reduce osteolysis by choosing bearing surface materials with reduced wear properties (such as metal-on-metal) should be balanced by awareness that reducing particle size may increase biological activity. Finally, although therapeutic agents against proinflammatory mediators [such as tumor necrosis factor (TNF)] and osteoclasts (bisphosphonates and molecules blocking RANKL signaling) have shown promise in animal models, no approved treatments are yet available to osteolysis patients. Considerable efforts are underway to develop such therapies, and to identify novel targets for therapeutic intervention.

Mechanotransduction of stretch-induced prostanoid release by fetal lung epithelial cells

Mechanical ventilation is the primary supportive treatment for infants and adults suffering from severe respiratory failure. Adverse mechanical ventilation (overdistension of the lung) triggers a proinflammatory response. Along with cytokines, inflammatory mediators such as bioactive lipids are involved in the regulation of the inflammatory response. The arachidonic acid pathway is a key source of bioactive lipid mediators, including prostanoids. Although ventilation has been shown to influence the production of prostanoids in the lung, the mechanotransduction pathways are unknown. Herein, we established that cyclic stretch of fetal lung epithelial cells, but not fibroblasts, can evoke an extremely sensitive, rapid alteration in eicosanoid metabolism through a cyclooxygenase (COX)-2 dependent mechanism. Cyclic stretch significantly increased PGI(2), PGF(2alpha), PGD(2), PGE(2), and thromboxane B(2) levels in the media of epithelial cells, but did not alter leukotriene B(4) or 12-hydroxyeicosatetraenoic acid levels. Inhibition of COX-2, but not COX-1, attenuated the cyclic stretch-induced PG increase in the media, suggesting that cyclic stretch primarily affected PG synthesis. Substrate (free arachidonic acid) availability for PG generation was increased because of a cyclic stretch-induced activation of cytosolic phospholipase A(2) (cPLA(2)) via an influx of extracellular calcium and phosphorylation by mitogen-activated protein kinase, p44/42MAPK. The data are compatible with cPLA(2) and COX-2 being intimately involved in regulating the injury response to adverse mechanical ventilation.

Impaction bone grafting with hydroxyapatite: increased femoral component stability in experiments using Sawbones

BACKGROUND

Substantial bone loss and bone defects increase the amount of allografting required in hip revision surgery. Thus, the use of a synthetic material to limit the amount of allograft tissue required for impaction grafting is desirable. We evaluated the potential of hydroxyapatite (HA) mixtures to provide initial mechanical stability to a polished tapered femoral stem.

MATERIAL AND METHODS

We determined the initial stability of a polished tapered femoral stem after reconstructing a cavitary femoral bone defect by impaction bone grafting with cement in Sawbones composite femurs. Three types of graft material were tested for their ability to improve initial rotational stability. The graft materials investigated were pure allograft, a mixture of 50% allograft and 50% hydroxyapatite (HA), and pure HA.

RESULTS

We found a statistically significant difference between the three groups as regards torsional micromotion and failure load.

INTERPRETATION

Our findings suggest that reconstruction of femoral bone defects with pure HA or a mixture of allograft and HA provides adequate initial stability for femoral revision arthroplasty using impaction grafting.

Bench-to-bedside review: Biotrauma and modulation of the innate immune response

The innate immune network is responsible for coordinating the initial defense against potentially noxious stimuli. This complex system includes anatomical, physical and chemical barriers, effector cells and circulating molecules that direct component and system interactions. Besides the direct effects of breaching pulmonary protective barriers, cyclic stretch generated during mechanical ventilation (MV) has been implicated in the modulation of the innate immunity. Evidence from recent human trials suggests that controlling MV-forces may significantly impact outcome in acute respiratory distress syndrome. In this paper, we explore the pertinent evidence implicating biotrauma caused by cyclic MV and its effect on innate immune responses.