Comparison of structure, strength and cytocompatibility of a fibrin matrix supplemented either with tranexamic acid or aprotinin

The tick and I: Parasite-host interactions between ticks and humans

Ticks, particularly hard ticks (Ixodidae), which are among the most important vectors of dangerous infectious agents, feed on their hosts for extended periods of time. With this lifestyle, numerous adaptations have evolved in ticks and their hosts, the pharmacological importance of which is increasingly being recognized. Many bioactive substances in tick saliva are being considered as the basis of new drugs. For example, components of tick cement can be developed into tissue adhesives or wound closures. Analgesic and antipruritic salivary components inhibit histamine or bradykinin, while other tick-derived molecules bind opioid or cannabinoid receptors. Tick saliva inhibits the extrinsic, intrinsic, or common pathway of blood coagulation with implications for the treatment of thromboembolic diseases. It contains vasodilating substances and affects wound healing. The broad spectrum of immunomodulatory and immunosuppressive effects of tick saliva, such as inhibition of chemokines or cellular immune responses, allows development of drugs against inflammation in autoimmune diseases and/or infections. Finally, modern vaccines against ticks can curb the spread of serious infections. The medical importance of the complex tick-host interactions is increasingly being recognized and translated into first clinical applications. Using selected examples, an overview of the mutual adaptations of ticks and hosts is given here, focusing on their significance to medical advance.

Safety and Efficacy of Local Tranexamic Acid for the Prevention of Surgical Bleeding in Soft-Tissue Surgery: A Review of the Literature and Recommendations for Plastic Surgery

Background:

Although high-bleed surgery routinely utilizes the antifibrinolytic drug tranexamic acid, most plastic surgical procedures are conducted in soft tissue with low-volume bleeding. Unease regarding possible systemic adverse effects prevents widespread systemic use, but local use of tranexamic acid is gaining popularity among plastic surgeons. Randomized controlled trials on topical use of tranexamic acid are mainly from high-bleed surgeries, and few studies address the effect in soft tissue. This article reviews the scientific evidence regarding local use of tranexamic acid in soft-tissue surgery, discusses pharmacological effects and possible adverse reactions, and presents recommendations for use in plastic surgery.

Methods:

A systematic search of databases for studies on local use of tranexamic acid in soft-tissue surgery was performed. Randomized controlled trials were included for a systematic review on effect; a narrative review regarding other clinically relevant aspects is based on extensive literature searches combined with the authors’ own research.

Results:

Fourteen randomized controlled trials, including 1923 patients, were included in the systematic review on local use of tranexamic acid in soft-tissue surgery.

Conclusions:

Local use of tranexamic acid may reduce blood loss comparably to intravenous prophylactic use with negligible risk of systemic adverse effects, but high-quality randomized controlled trials are few. Prolonged exposure to high local concentrations is discouraged, and direct contact with the central nervous system may cause seizures. No single superior means of administration or dosage is supported in the literature, and lowest effective dose is unknown. There may not be one single ideal dosing regimen, but rather many possibilities adaptable for different surgical situations.

Cytotoxicity and effect on wound re-epithelialization after topical administration of tranexamic acid

Background

Topical administration of tranexamic acid (TXA) reduces bleeding from surgical wounds similarly to intravenous use, but with negligible risk of adverse systemic events. Topical use is expanding, but is off‐label. Surgeons lack guidelines regarding safe topical dosages and modes of administration. The effects of topical TXA on skin cells and wound healing are unknown. This study investigated whether topical TXA might be cytotoxic or affect wound re‐epithelialization.

Methods

Human keratinocytes and fibroblast cell cultures and an ex vivo human skin wound model were subjected to both short (limited) and long (chronic) exposure to various clinically relevant concentrations of TXA to mimic different modalities of topical administration. Cytotoxicity and effects on wound re‐epithelialization were evaluated.

Results

In cell culture, toxicity from chronic exposure was associated with increasing concentration and exposure time. Limited exposure to TXA did not cause significant cytotoxicity even at high concentrations. Re‐epithelialization was completely absent in wounds chronically exposed to TXA concentrations of 25 mg/ml or above, and 50–100 mg/ml induced epidermolysis of normal epithelium, possibly by a non‐toxic mechanism. Wound re‐epithelialization was slightly delayed, but not impaired, by limited exposure to 100 mg/ml or chronic exposure to 6·25 mg/ml.

Conclusion

Although short exposure to even high concentrations of topical TXA seems well tolerated in vitro, prolonged exposure can be cytotoxic and may affect wound re‐epithelialization. Surgeons should adjust the TXA concentration to the planned mode of topical administration in clinical practice.

Fibrin-based delivery strategies for acute and chronic wound healing

Fibrin, a natural hydrogel, is the end product of the physiological blood coagulation cascade and naturally involved in wound healing. Beyond its role in hemostasis, it acts as a local reservoir for growth factors and as a provisional matrix for invading cells that drive the regenerative process. Its unique intrinsic features do not only promote wound healing directly via modulation of cell behavior but it can also be fine-tuned to evolve into a delivery system for sustained release of therapeutic biomolecules, cells and gene vectors. To further augment tissue regeneration potential, current strategies exploit and modify the chemical and physical characteristics of fibrin to employ combined incorporation of several factors and their timed release. In this work we show advanced therapeutic approaches employing fibrin matrices in wound healing and cover the many possibilities fibrin offers to the field of regenerative medicine.

Is tranexamic acid toxic to articular cartilage when administered topically?

Aims

The intra-articular administration of tranexamic acid (TXA) has been shown to be effective in reducing blood loss in unicompartmental knee arthroplasty and anterior cruciate reconstruction. The effects on human articular cartilage, however, remains unknown. Our aim, in this study, was to investigate any detrimental effect of TXA on chondrocytes, and to establish if there was a safe dose for its use in clinical practice. The hypothesis was that TXA would cause a dose-dependent damage to human articular cartilage.

Materials and Methods

The cellular morphology, adhesion, metabolic activity, and viability of human chondrocytes when increasing the concentration (0 mg/ml to 40 mg/ml) and length of exposure to TXA (0 to 12 hours) were analyzed in a 2D model. This was then repeated, excluding cellular adhesion, in a 3D model and confirmed in viable samples of articular cartilage.

Results

Increasing concentrations above 20 mg/ml resulted in atypical morphology, reduced cellular adhesion and metabolic activity associated with increased chondrocyte death. However, the cell matrix was not affected by the concentration of TXA or the length of exposure, and offered cellular protection for concentrations below 20 mg/ml.

Conclusion

These results show that when in vitro chondrocytes are exposed to higher concentrations of TXA, such as that expected following recommended intra-articular administration, cytotoxicity is observed. This effect is dose-dependent, such that a tissue concentration of 10 mg/ml to 20 mg/ml could be expected to be safe. Cite this article: Bone Joint J 2018;100-B:404–12.

Human Kunitz-type protease inhibitor engineered for enhanced matrix retention extends longevity of fibrin biomaterials

Aprotinin is a broad-spectrum serine protease inhibitor used in the clinic as an anti-fibrinolytic agent in fibrin-based tissue sealants. However, upon re-exposure, some patients suffer from hypersensitivity immune reactions likely related to the bovine origin of aprotinin. Here, we aimed to develop a human-derived substitute to aprotinin. Based on sequence homology analyses, we identified the Kunitz-type protease inhibitor (KPI) domain of human amyloid-β A4 precursor protein as being a potential candidate. While KPI has a lower intrinsic anti-fibrinolytic activity than aprotinin, we reasoned that its efficacy is additionally limited by its fast release from fibrin material, just as aprotinin's is. Thus, we engineered KPI variants for controlled retention in fibrin biomaterials, using either covalent binding through incorporation of a substrate for the coagulation transglutaminase Factor XIIIa or through engineering of extracellular matrix protein super-affinity domains for sequestration into fibrin. We showed that both engineered KPI variants significantly slowed plasmin-mediated fibrinolysis in vitro, outperforming aprotinin. In vivo, our best engineered KPI variant (incorporating the transglutaminase substrate) extended fibrin matrix longevity by 50%, at a dose at which aprotinin did not show efficacy, thus qualifying it as a competitive substitute of aprotinin in fibrin sealants.

Efficacy of bubaline fibrin glue on full-thickness pinch and punch skin grafting in a pig

Fibrin glue, which is formed from the action of thrombin (a serine protease) on fibrinogen, has been developed for use as an adhesive to increase the success of skin graft surgery. The objective of this study was to evaluate if bubaline fibrin glue would promote skin graft survival in pigs. The grafting was divided into two steps. First, granulation wound preparation was performed in a healthy swine by creating four full-skin depth wounds (3 × 12 cm²) at the dorsal part of the loin area on each side. Second, pinch and punch skin grafting, where eight skin discs (0.6 cm diameter) were regularly placed (0.6 cm distance apart) in the granulation tissue bed of each wound, was performed 5 days later. The bubaline fibrin glue was added prior to application of the 16 skin graft discs in two of the wounds, while no glue was added to the other 16 skin graft discs in the other two wounds. The number of surviving graft pieces and histological examination was evaluated after 3, 7, and 14 days post-operation and compared by pairing between the control and the bubaline fibrin glue groups. The number of grafts that remained at 3 and 7 days post-operation and the number of new microvessels at 3 days post-operation were significantly higher ( p < 0.05) in the bubaline fibrin glue group than in the control group. However, there was no significant difference in the number of fibroblasts, the intensity of scarring and the intensity of inflammation between the two groups, except for the significantly lower intensity of inflammation at 7 days post-operation in the bubaline fibrin glue group. In conclusion, bubaline fibrin glue has the advantage of decreasing the skin graft loss by approximately 31.3-37.5% compared with the control group and also promotes angiogenesis.

Thrombin based gelatin matrix and fibrin sealant mediated clot formation in the presence of clopidogrel

BACKGROUND

Platelet inhibitors are commonly used to reduce the risk of atherothrombotic events. The aim of this study was to determine the impact of platelet inhibitors, specifically clopidogrel and aspirin, on clot kinetics, strength, and/or structure during the use of thrombin based gelatin matrices and fibrin sealants.

METHODS

Blood was collected and heparinized from donors on clopidogrel (and aspirin) and age matched control donors. Blood component analysis, whole blood platelet aggregometry, and activated clotting time (ACT) were used to monitor compliance to therapy and identify any differences between donor groups. Clot kinetics and strength were analyzed using thrombelastography (TEG). Field Emission Scanning Electron Microscopy (FESEM) was used to analyze clot structure.

RESULTS

Blood component profiles were similar for both donor groups. Aggregometry indicated that aggregation response to adenosine diphosphate (ADP) for clopidogrel donors was 12% of that for the controls (p = 0.0021), an expected result of clopidogrel induced platelet inhibition. However, blood from both donor groups had an elevated thrombin induced aggregation response. Heparinization of donor blood resulted in similarly elevated ACTs for both donor groups. TEG results indicated similar clot kinetics and strength between clopidogrel and control donor groups for blood alone and when clotting was induced using thrombin based gelatin matrices and fibrin sealants. FESEM images supported TEG findings in that similar morphologies were observed in ex vivo formed clots from both donor groups when thrombin based gelatin matrices and fibrin sealants were used.

CONCLUSION

These results suggest that platelet inhibitors do not negatively impact clot kinetics, strength, and structure when clotting is initiated with thrombin based gelatin matrices and fibrin sealants.

Comparison of commercial fibrin sealants in facelift surgery: a prospective study

Background

The aim of this study was to compare the effects of two types of fibrin glue in patients undergoing facelift surgery.

Methods

A prospective, controlled “right-left side” study was carried out in 20 patients. The two fibrin sealants used were Quixil® and Tissucol®. The two sealants were used at the same time, ie, one on one side of the face and the other on the contralateral side. Comparisons were made with regard to rates of hematoma and seroma, degree of induration, edema, ecchymosis, pain levels, and patient satisfaction.

Results

The results were almost equivalent. The only exception was a significant (40 mL) hematoma in a patient treated with Quixil. Bleeding was most likely due to a sudden rise in blood pressure during the immediate postoperative period. However, it must be emphasized that, while Tissucol actually seals the undermined area, thus virtually eliminating the dead space, Quixil acts differently, in that its effectiveness in preventing hematoma is linked mainly to its hemostatic effect.

Conclusion

The two fibrin sealants used were nearly identical with regard to patient safety and quality of the result. Nevertheless, it is noted that, while Tissucol has both hemostatic and “gluing” effects, Quixil is mainly effective in securing hemostasis.

Wound coverage technologies in burn care: novel techniques

Improvements in burn wound care have vastly decreased morbidity and mortality in severely burned patients. Development of new therapeutic approaches to increase wound repair has the potential to reduce infection, graft rejection, and hypertrophic scarring. The incorporation of tissue-engineering techniques, along with the use of exogenous proteins, genes, or stem cells to enhance wound healing, heralds new treatment regimens based on the modification of already existing biological activity. Refinements to surgical techniques have enabled the creation of protocols for full facial transplantation. With new technologies and advances such as these, care of the severely burned will undergo massive changes over the next decade. This review centers on new developments that have recently shown great promise in the investigational arena.

Fibrin chain cross-linking, fibrinolysis, and in vivo sealing efficacy of differently structured fibrin sealants

In this study, we compared the sealing characteristics and efficacy of a fibrin sealant with reduced plasminogen (FS-rplg) and a fibrin sealant with aprotinin as a fibrinolysis inhibitor (FS-apr). The relevant sealing characteristics including clot structure, fibrin chain cross-linking, and clot lysis were tested in the laboratory. The sealing efficacy was then investigated in a follow-up animal model to determine differences in the in vivo sealing properties. A total of 46 animals were available for the final analysis with 23 animals in each treatment arm. In conclusion, we saw differences in vitro between FS-rplg and FS-apr in ultrastructure and α-chain cross-linking rates as well as in the rate of fibrinolysis. These differences may explain the significantly enhanced sealing efficacy in FS-apr compared to FS-rplg shown in vivo in a rabbit intestinal model.

Allogeneic single-donor cryoseal produced from fresh-frozen quarantine apheresis plasma as alternative for multidonor or autologous fibrin sealants

BACKGROUND

Fibrin sealant is a human blood product consisting of two components: cryoprecipitate and thrombin. Commercial fibrin sealants are produced from multidonors, increasing the viral risk, and contain fibrinolytic inhibitors such as tranexamic acid or bovine aprotinin. Autologous fibrin sealants reduce the viral risk and are mostly produced during a surgical procedure or well in advance. Alternatively, the allogeneic single-donor fibrin sealant cryoseal can be used. In this study cryoseal was characterized and the manufacturing consistency of the production process was investigated.

STUDY DESIGN AND METHODS

Cryoseal was produced from plasma collected on apheresis machines using a commercial device. In a research setting the protein composition and recovery were determined. Also, the manufacturing consistency of the production process was tested in a research setting as well as in a routine setting.

RESULTS

In the research setting all produced cryoseal met the quality control requirements of a clotting time of less than 10 seconds and the presence of Factor (F)XIII (qualitative). In the routine setting, one procedure per year did not meet these requirements. The protein composition showed the following mean ± standard deviation (%recovery) results: thrombin 25.7 ± 11.1 IU/mL, fibrinogen 19.9 ± 4.6 (15%) mg/mL, FVIII 15.6 ± 5.4 (44%) IU/mL, FXIII 2.7 ± 0.7 (6%) IU/mL, and plasminogen 1.8 ± 0.2 (4%) U/mL. In both research and routine settings the production process resulted in a consistent product.

CONCLUSION

The cryoseal manufacturing process resulted in a consistent product, which meets the predetermined specifications. The single-donor origin and the absence of fibrinolytic inhibitors make cryoseal a good alternative for multidonor and autologous fibrin sealants.

Autologous valve replacement-CD133+ stem cell-plus-fibrin composite-based sprayed cell seeding for intraoperative heart valve tissue engineering

OBJECTIVE

The development of biological valve prostheses with lifetime native-like performance and optimal host engraftment is an ultimate goal of heart valve tissue engineering. We describe a new concept for autologous graft coating based on a CD133(+)-stem-cells-plus-fibrin (SC+F) complex processed from bone marrow and peripheral blood of a single patient.

METHODS

CD133(+)-SC (1 × 10(6) cells/mL) from human bone marrow and autologous fibrin (20 mg/mL) were administered simultaneously via spray administration using the novel Vivostat Co-Delivery System. During static cultivation, SC+F performance was monitored for 20 days after delivery and compared with controls. For dynamic testing SC+F-composite was sprayed on a decellularized porcine pulmonary valve and transferred to a bioreactor under pulsatile flow conditions for 7 days.

RESULTS

Static cultivation of SC+F-composite induced significant improvements in stem cell proliferation as compared with controls. For dynamic testing, microscopic analyses on a smooth engineered heart valve surface detected homogenous distribution of stem cells. Ultrasonic analysis revealed native-like valve performance. Applied CD133(+) stem cells differentiated into endothelial-like cells positive for CD31 and vascular endothelial growth factor receptor 2 and engrafted the valve. However, occasional delamination was observed.

CONCLUSION

SC+F serves as an excellent autologous matrix for intraoperative tissue engineering of valve prostheses promising optimal in vivo integration. However, stability remains an issue.

Cell Compatibility of Fibrin Sealants: In Vitro Study with Cells Involved in Soft Tissue Repair

Fibrin sealants can be used to support tissue regeneration or as vehicles for delivery of cells in tissue engineering. Differences in the composition of fibrin sealants, however, could determine the success of such applications. The results presented in this article show clear differences between Fibrin sealant A (FS A) clots and Fibrin sealant B (FS B) clots with respect to their compatibility with primary human cells involved in soft tissue repair. FS A clots, which are characterized by a physiological coarse fibrin structure, promoted attachment, spreading, and proliferation of keratinocytes, fibroblasts, and endothelial cells. In contrast, FS B clots displaying a fine to medium clot structure failed to support spreading of all three cell types. Adhesion of keratinocytes was decreased on FS B clots compared to FS A clots after 3 h incubation, whereas number of attached fibroblasts and endothelial cells was initially comparable between the two fibrin sealants. However, all three cell types proliferated on FS A clots but no sustained proliferation was detected on FS B clots. We further demonstrate that the observed differences between FS A and B clots are partly based upon 1 M sodium chloride extractable constituents, like thrombin, and partly on nonextractable constituents or the fibrin structure. In conclusion, our in vitro results demonstrate that FS A clots serve as a provisional matrix that encourages adhesion and growth of keratinocytes, fibroblasts, and endothelial cells. Therefore, FS A seems to be well suited for applications in tissue engineering.

Regulating fibrinolysis to engineer skeletal muscle from the C2C12 cell line

Muscles engineered from transformed cells would be a powerful model for the study of muscle physiology by allowing long-term in vitro studies of muscle adaptation. However, previously described methods either take >5 weeks to produce a tissue or use collagen as a scaffold, which decreases the specific force of the muscle, making it hard to measure the function of the constructs. The aim of this study was to rapidly engineer muscle using the C2C12 cell line in fibrin, which has a stiffness similar to muscle tissue, allowing accurate functional testing. Both the protease inhibitor aprotinin and the natural cross-linker genipin increased the length of time that muscle could be cultured, with genipin increasing the time in culture to 10 weeks. The function of the tissues was significantly affected by the batch of serum (64-78%) or thrombin (41%), the differentiation medium (78%), and the seeding protocol (38%), but was unaffected by initial cell number. Strikingly, different C2C12 clones produced up to a 3.6-fold variation in force production. Under optimal conditions, the tissues form in 10.4+/-0.3 days and remain fully functional for 5 weeks over which time they continue to mature. The optimized model described here provides rapid, reliable, and functional tissues that will be useful in the study of skeletal muscle physiology.

Controlled release of substances bound to fibrin-anchors or of DNA

Fibrin sealants have been proposed as depot matrices for substances due to their biocompatibility, advantageous biological properties, and widespread use in wound healing. This study showed possibilities for a continuous and controlled release of pharmaceutically active substances out of a fibrin matrix. Substances of interest were linked to naturally occuring fibrin-anchors, (i) thrombin, (ii) fibronectin, and (iii) DNA. Fibronectin and thrombin bind fibrin by a specific binding moiety and DNA by charge. Fibrin clots were prepared from Tisseel Fibrin Sealant (Baxter AG, Vienna) by mixing 100 mg/ml fibrinogen, the substance of interest, and 4 U/ml of thrombin. Chemical crosslinking of proteins was performed with EDC using standard reaction conditions. Modification of proteins with biotin and PPACK was performed with N-hydroxysuccinimid activated compounds. With fibrin-anchors pharmaceutically active substances, i.e., tumor necrosis factor (TNF), albumin, and plasmid-DNA, were continously released over 10 days. In conclusion, the naturally occuring proteins fibronectin and thrombin with a fibrin binding moiety or DNA can be used as fibrin-anchors.

A porcine model of full-thickness burn, excision and skin autografting

Acute burn wounds often require early excision and adequate coverage to prevent further hypothermia, protein and fluid losses, and the risk of infection. Meshed autologous skin grafts are generally regarded as the standard treatment for extensive full-thickness burns. Graft take and rate of wound healing, however, depend on several endogenous factors. This paper describes a standardized reproducible porcine model of burn and skin grafting which can be used to study the effects of topical treatments on graft take and re-epithelialization. Procedures provide a protocol for successful porcine burn wound experiments with special focus on pre-operative care, anesthesia, burn allocation, excision and grafting, postoperative treatment, dressing application, and specimen collection. Selected outcome measurements include percent area of wound closure by planimetry, wound assessment using a clinical assessment scale, and histological scoring. The use of this standardized model provides burn researchers with a valuable tool for the comparison of different topical drug treatments and dressing materials in a setting that closely mimics clinical reality.