Human osteoarthritic synovium impacts chondrogenic differentiation of mesenchymal stem cells via macrophage polarisation state.

OBJECTIVE: Mesenchymal stem cells (MSCs) are a promising cell type for the repair of damaged cartilage in osteoarthritis (OA). However, OA synovial fluid and factors secreted by synovium impede chondrogenic differentiation of MSCs, and the mechanism responsible for this effect remains unclear. In this study, we sought to investigate whether M1 and M2 synovial macrophages can contribute to the inhibition of MSC chondrogenesis. DESIGN: The constitution of synovial macrophage subsets was analysed by immunohistochemical staining of human OA synovium sections for CD86 (M1 marker) and CD206 (M2 marker). To assess the effect of synovial macrophages on chondrogenesis, collagen type II (COL2) and aggrecan (ACAN) gene expression were compared between MSCs undergoing chondrogenic differentiation in medium conditioned (CM) by human OA synovial explants, human synovial macrophages and fibroblasts, or peripheral blood derived primary human monocytes differentiated towards an M1 or M2 phenotype. RESULTS: OA synovium contained both M1 and M2 macrophages. Medium conditioned by synovial macrophages (CD45 + plastic adherent cells) down-regulated chondrogenic gene expression by MSCs. Additionally, CM of M1 polarised monocytes significantly decreased COL2 and ACAN gene expression by MSCs; this effect was not observed for treatment with CM of M2 polarised monocytes. CONCLUSION: MSC chondrogenesis is inhibited by OA synovium CM through factors secreted by synovial macrophages and our findings suggest that M1 polarised subsets are potential mediators of this anti-chondrogenic effect. Modulation of macrophage phenotype may serve as a beneficial strategy to maximise the potential of MSCs for efficient cartilage repair.

In vitro model to study the biomaterial-dependent reaction of macrophages in an inflammatory environment.

BACKGROUND: Macrophages play an important role in the reaction to biomaterials, which sometimes have to be used in a surgical field at risk of contamination. The macrophage phenotype in reaction to biomaterials in an inflammatory environment was evaluated in both an in vivo and in vitro setting. METHODS: In the in vivo setting, polypropylene (PP) biomaterial was implanted for 28 days in the contaminated abdominal wall of rats, and upon removal analysed by routine histology as well as immunohistochemistry for CD68 (marker for macrophages), inducible nitric oxide synthase (iNOS - a marker for proinflammatory M1 macrophages) and CD206 (marker for anti-inflammatory M2 macrophages). For the in vitro model, human peripheral blood monocytes were cultured for 3 days on biomaterials made from PP, collagen (COL), polyethylene terephthalate (PET) and PET coated with collagen (PET+COL). These experiments were performed both with and without lipopolysaccharide and interferon γ stimulation. Secretion of both M1- and M2-related proteins was measured, and a relative M1/M2 index was calculated. RESULTS: In vivo, iNOS- and CD206-positive cells were found around the fibres of the implanted PP biomaterial. In vitro, macrophages on both PP and COL biomaterial had a relatively low M1/M2 index. Macrophages on the PET biomaterial had a high M1/M2 index, with the highest increase of M1 cytokines in an inflammatory environment. Macrophages on the PET+COL biomaterial also had a high M1/M2 index. CONCLUSION: Macrophages in an inflammatory environment in vitro still react in a biomaterial-dependent manner. This model can help to select biomaterials that are tolerated best in a surgical environment at risk of contamination.

Biologic meshes are not superior to synthetic meshes in ventral hernia repair: an experimental study with long-term follow-up evaluation.

BACKGROUND: In laparoscopic incisional hernia repair, direct contact between the prosthesis and the abdominal viscera is inevitable, which may lead to an inflammatory reaction resulting in abdominal adhesion formation. This study compared five different synthetic and biologic meshes in terms of adhesion formation, shrinkage, incorporation, and histologic characteristics after a period of 30 and 90 days. METHODS: In 85 rats, a mesh was positioned intraperitoneally in direct contact with the viscera. Five different meshes were implanted: Prolene (polypropylene), Parietex composite (collagen-coated polyester), Strattice (porcine dermis, non-cross-linked), Surgisis (porcine small intestine submucosa, non-cross-linked), and Permacol (porcine dermis, cross-linked). The meshes were tested in terms of adhesion formation, shrinkage, and incorporation after a period of 30 and 90 days. Additionally, collagen formation after 90 days was determined. RESULTS: Significantly less adhesion formation was observed with Parietex composite (5 %; interquartile range [IQR], 2-5 %) and Strattice (5 %; IQR, 4-10 %) in the long term. In contrast, organs were attached to Permacol with four of seven meshes (57 %), and adhesion coverage of Surgisis mesh was present in 66 % (IQR, 0-100 %) of the cases. After 90 days, the best incorporation was seen with the Parietex composite mesh (79 %; IQR, 61-83 %). After 90 days, major alterations in adhesion formation were seen compared with 30 days. Histologically, Strattice and Parietex composite showed a new mesothelial layer on the visceral side of the mesh. Microscopic degradation and new collagen formation were seen in the Surgisis group. CONCLUSIONS: Parietex composite mesh demonstrated the best long-term results compared with all the other meshes. The biologic non-cross-linked mesh, Strattice, showed little adhesion formation and moderate shrinkage but poor incorporation. Biologic meshes are promising, but varying results require a more detailed investigation and demonstrate that biologic meshes are not necessarily superior to synthetic meshes. The significant changes that take place between 30 and 90 days should lead to careful interpretation of short-term experimental results.

A culture model to analyze the acute biomaterial-dependent reaction of human primary macrophages.

Macrophages are important in foreign body reactions. We devised a culture model with human primary macrophages to evaluate the acute response of macrophages to biomaterials. First we selected proteins representative for pro-inflammatory (M1) or anti-inflammatory/repair (M2) response of monocytes isolated from blood of healthy human donors by exposing them to LPS+IFNγ or IL-4. A relative M1/M2 index was calculated using IL-1ß, IL-6, tumor necrosis factor (TNF)α, monocyte chemotactic protein (MCP)-3 and macrophage inflammatory protein (MIP)-1α as M1 markers, and IL-1 receptor antagonist (IL-1RA), CCL18, regulated and normal T-cell expressed and secreted (RANTES), and macrophage-derived chemokine (MDC) as M2 markers. Then monocytes were cultured for 3days on 4 materials selected for known different foreign body reactions: Permacol™, Parietex™ Composite, multifilament polyethylene terephthalate and multifilament polypropylene. Macrophages on polypropylene produced high levels of anti-inflammatory proteins with a low M1/M2 index. Macrophages on Parietex™ Composite produced high levels of inflammatory and anti-inflammatory proteins, with a high M1/M2 index. Macrophages on polyethylene terephthalate also resulted in a high M1/M2 index. Macrophages on Permacol™ produced a low amount of all proteins, with a low M1/M2 index. This model with human primary macrophages and the panel of read-out parameters can be used to evaluate the acute reaction of macrophages to biomaterials in vitro to get more insight in the foreign body reaction.

Experimental study on synthetic and biological mesh implantation in a contaminated environment.

BACKGROUND: Implantation of meshes in a contaminated environment can be complicated by mesh infection and adhesion formation. METHODS: The caecal ligation and puncture model was used to induce peritonitis in 144 rats. Seven commercially available meshes were implanted intraperitoneally: six non-absorbable meshes, of which three had an absorbable coating, and one biological mesh. Mesh infection, intra-abdominal abscess formation, adhesion formation, incorporation and shrinkage were evaluated after 28 and 90 days. Histological examination with haematoxylin and eosin and picrosirius red staining was performed. RESULTS: No mesh infections occurred in Sepramesh(®) , Omyramesh(®) and Strattice(®) . One mesh infection occurred in Parietene(®) and Parietene Composite(®) . Significantly more mesh infections were found in C-Qur(®) (15 of 16; P ≤ 0·006) and Dualmesh(®) (7 of 15; P ≤ 0·035). Sepramesh(®) showed a significant increase in adhesion coverage from 12·5 per cent at 28 days to 60·0 per cent at 90 days (P = 0·010). At 90 days there was no significant difference between median adhesion coverage of Parietene Composite(®) (35·0 per cent), Omyramesh(®) (42·5 per cent), Sepramesh(®) (60·0 per cent) and Parietene(®) (72·5 per cent). After 90 days the adhesion coverage of Strattice(®) was 5·0 per cent, and incorporation (13·4 per cent) was significantly poorer than for other non-infected meshes (P ≤ 0·009). Dualmesh(®) showed shrinkage of 63 per cent after 90 days. CONCLUSION: Parietene Composite(®) and Omyramesh(®) performed well in a contaminated environment. Strattice(®) had little adhesion formation and no mesh infection, but poor incorporation. Some synthetic meshes can be as resistant to infection as biological meshes.