In Vitro and In Vivo Effects of IGF-1 Delivery Strategies on Tendon Healing: A Review

Tendon injuries suffer from a slow healing, often ending up in fibrovascular scar formation, leading to inferior mechanical properties and even re-rupture upon resumption of daily work or sports. Strategies including the application of growth factors have been under view for decades. Insulin-like growth factor-1 (IGF-1) is one of the used growth factors and has been applied to tenocyte in vitro cultures as well as in animal preclinical models and to human patients due to its anabolic and matrix stimulating effects. In this narrative review, we cover the current literature on IGF-1, its mechanism of action, in vitro cell cultures (tenocytes and mesenchymal stem cells), as well as in vivo experiments. We conclude from this overview that IGF-1 is a potent stimulus for improving tendon healing due to its inherent support of cell proliferation, DNA and matrix synthesis, particularly collagen I, which is the main component of tendon tissue. Nevertheless, more in vivo studies have to be performed in order to pave the way for an IGF-1 application in orthopedic clinics. Keywords: tenocytes; stem cells; growth factor; collagen; PI3K/Akt/mTOR pathway; Ras-MAPK pathway; PLC pathwa

Delineation of the healthy rabbit tongue by immunohistochemistry - A technical note

In the oral cavity the tongue is an important muscular organ that supports the swallowing of food and liquids. It is responsible for the sense of taste, based on the many different taste buds it contains. Research in the field of tongue diseases demands for suitable preclinical models. The healthy rabbit tongue may therefore serve as baseline and reference for the pathological situation. With this consideration, we covered the fixation and histological stainings as well as the immunohistochemical labelling of the healthy rabbit tongue. In this technical note, initial choice of the fixative is discussed, with a comparison of formalin fixation and subsequent paraffin embedding versus cryopreservation. Moreover, we delineate the effect of an antigen retrieval step for formalin fixation by several examples. Finally, we provide ECM markers collagen I, collagen III, fibronectin, α-SMA and elastin staining as well as ki67 for proliferative status and PAR-2 protein expression as a marker for inflammatory status and nociception in tongue sections, mainly from the tongue body. Technically, we found superiority of paraffin sections for collagen I, collagen III, fibronectin, ki67 and α-SMA labelling, for selected detections systems. As for ECM components, the lamina propria was very rich in collagen and fibronectin, while the muscular body of the tongue showed only collagen and fibronectin positive areas between the muscle fibers. Moreover, α-SMA was clearly expressed in the walls of arteries and veins. The inflammatory marker PAR-2 on the other hand was prominently expressed in the salivary glands and to some extent in the walls of the vessels. Particular PAR-2 expression was found in the excretory ducts of the tongue. This technical note has the aim to provide baseline images that can be used to compare the pathological state of the diseased rabbit tongue as well as for inter-species comparison, such as mouse or rat tongue. Finally, it can be used for the comparison with the human situation

Hyaluronic acid/PEO electrospun tube reduces tendon adhesion to levels comparable to native tendons - An in vitro and in vivo study

A major problem after tendon injury is adhesion formation to the surrounding tissue leading to a limited range of motion. A viable strategy to reduce adhesion extent is the use of physical barriers that limit the contact between the tendon and the adjacent tissue. The purpose of this study was to fabricate an electrospun bilayered tube of hyaluronic acid/polyethylene oxide (HA/PEO) and biodegradable DegraPol® (DP) to improve the anti-adhesive effect of the implant in a rabbit Achilles tendon full laceration model compared to a pure DP tube. Additionally, the attachment of rabbit tenocytes on pure DP and HA/PEO containing scaffolds was tested and Scanning Electron Microscopy, Fourier-transform Infrared Spectroscopy, Differential Scanning Calorimetry, Water Contact Angle measurements, and testing of mechanical properties were used to characterize the scaffolds. In vivo assessment after three weeks showed that the implant containing a second HA/PEO layer significantly reduced adhesion extent reaching levels comparable to native tendons, compared with a pure DP implant that reduced adhesion formation only by 20 %. Tenocytes were able to attach to and migrate into every scaffold, but cell number was reduced over two weeks. Implants containing HA/PEO showed better mechanical properties than pure DP tubes and with the ability to entirely reduce adhesion extent makes this implant a promising candidate for clinical application in tendon repair

Bioactive and Elastic Emulsion Electrospun DegraPol Tubes Delivering IGF-1 for Tendon Rupture Repair

Tendon injuries can result in two major drawbacks. Adhesions to the surrounding tissue may limit the range of motion, while fibrovascular scar formation can lead to poor biomechanical outcomes. Prosthetic devices may help to mitigate those problems. Emulsion electrospinning was used to develop a novel three-layer tube based on the polymer DegraPol (DP), with incorporated insulin-like growth factor-1 (IGF-1) in the middle layer. Scanning electron microscopy was utilized to assess the fiber diameter in IGF-1 containing pure DP meshes. Further characterization was performed with Fourier Transformed Infrared Spectroscopy, Differential Scanning Calorimetry, and water contact angle, as well as through the assessment of mechanical properties and release kinetics from ELISA, and the bioactivity of IGF-1 by qPCR of collagen I, ki67, and tenomodulin in rabbit Achilles tenocytes. The IGF-1-containing tubes exhibited a sustained release of the growth factor up to 4 days and showed bioactivity by significantly upregulated ki67 and tenomodulin gene expression. Moreover, they proved to be mechanically superior to pure DP tubes (significantly higher fracture strain, failure stress, and elastic modulus). The novel three-layer tubes intended to be applied over conventionally sutured tendons after a rupture may help accelerate the healing process. The release of IGF-1 stimulates proliferation and matrix synthesis of cells at the repair site. In addition, adhesion formation to surrounding tissue can be reduced due to the physical barrier

In Vitro and In Vivo Effects of IGF-1 Delivery Strategies on Tendon Healing: A Review

Tendon injuries suffer from a slow healing, often ending up in fibrovascular scar formation, leading to inferior mechanical properties and even re-rupture upon resumption of daily work or sports. Strategies including the application of growth factors have been under view for decades. Insulin-like growth factor-1 (IGF-1) is one of the used growth factors and has been applied to tenocyte in vitro cultures as well as in animal preclinical models and to human patients due to its anabolic and matrix stimulating effects. In this narrative review, we cover the current literature on IGF-1, its mechanism of action, in vitro cell cultures (tenocytes and mesenchymal stem cells), as well as in vivo experiments. We conclude from this overview that IGF-1 is a potent stimulus for improving tendon healing due to its inherent support of cell proliferation, DNA and matrix synthesis, particularly collagen I, which is the main component of tendon tissue. Nevertheless, more in vivo studies have to be performed in order to pave the way for an IGF-1 application in orthopedic clinics

Delineation of the healthy rabbit liver by immunohistochemistry - A technical note

Liver diseases pose a big global health problem and liver failure may result from viral infection, overnutrition or tumors. Studying pathologic liver tissue demands for accurate and specific histological stainings and immunohistochemical labellings, including chromogenic and fluorescent approaches. Moreover, a reliable set of healthy liver stainings and labellings are required, to provide a baseline or reference for the pathological situation. Here, we used the liver tissue of a healthy rabbit and compared different histological key steps, such as paraffin embedding after formalin fixation versus cryopreservation; or an antigen retrieval (AR) step in processing paraffin sections versus the same procedure without AR; or chromogenic with fluorescent detection system, respectively. Moreover, we provide images of serial sections, where we stained the same morphological structure with different markers, including collagen I, collagen III, fibronectin, α-SMA, elastin, protease-activated receptor-2 (PAR-2) which is an inflammation-related marker, ki67 for proliferating cells, and orcein (as negative control for pathological aberrations like Wilson disease). Differences between conditions were quantitatively assessed by measuring the colour intensity. Generally, we observed that cryosections exhibited a stronger signal intensity in immunohistochemically labelled sections than in paraffin sections; however, the strong staining got slurred, which sometimes hampered proper identification of morphological structures at higher magnifications. Moreover, there was a clear increase in signal intensity for paraffin sections when an AR step was performed compared to condition without AR. Results for mouse isotype staining as a negative control clearly supported those findings. Different stainings of the portal triad, the central vein and the bile ducts revealed a clear-cut distribution of extracellular matrix components, with prominent fibronectin and elastin around the lumen of the central vein as well as a patchy PAR-2 expression. As for the bile ducts, complete absence of α-SMA and PAR-2 was found at the margins, however, collagen I expression and elastin were positive and showed a strong signal. Like this, we provide useful and valuable reference images for researchers using the rabbit liver model. It may help to decide which of the immunohistochemical protocols are valuable to reach a certain aim and which protocols lead to the best visualization of the target structure

Pro-angiogenic and antibacterial copper containing nanoparticles in PLGA/amorphous calcium phosphate bone nanocomposites

Large bone defects after trauma demand for adequate bone substitutes. Bone void fillers should be antibacterial and pro-angiogenic. One viable option is the use of composite materials like the combination of PLGA and amorphous calcium phosphate (aCaP). Copper stimulates angiogenesis and has antibacterial qualities. Either copper oxide (CuO) nanoparticles (NPs) were therefore added to PLGA/aCaP/CuO in different concentrations (1, 5 and 10 w/w %) or copper-doped tricalcium phosphate NPs (TCP with 2% of copper) were electrospun into PLGA/CuTCP nanocomposites. Bi-layered nanocomposites of PLGA/aCaP with different copper NPs (CuO or TCP) and a second layer of pristine PLGA were fabricated. Two clinical bacterial isolates (Staphylococcus aureus and Staphylococcus epidermidis) were used to assess antibacterial properties of the copper-containing materials. For angiogenesis, the chorioallantoic membrane (CAM) assay of the chicken embryo was performed. The higher the CuO content, the higher were the antibacterial properties, with 10 % CuO reducing bacterial adhesion most effectively. Vessel and cell densities were highest in the 5 % CuO containing scaffolds, while tissue integration was more pronounced at lower CuO content. The PLGA/aCaP/CuO (1 % CuO) behaved similar like PLGA/CuTCP in all angiogenic and antibacterial readouts, based on the same copper fraction. We conclude that CuO NPs or CuTCP NPs are useful components to increase angiogenic properties of nanocomposites and at the same time exhibiting antibacterial characteristics