Inflammatory and regenerative processes in bioresorbable synthetic pulmonary valves up to two years in sheep-Spatiotemporal insights augmented by Raman microspectroscopy.

In situ heart valve tissue engineering is an emerging approach in which resorbable, off-the-shelf available scaffolds are used to induce endogenous heart valve restoration. Such scaffolds are designed to recruit endogenous cells in vivo, which subsequently resorb polymer and produce and remodel new valvular tissue in situ. Recently, preclinical studies using electrospun supramolecular elastomeric valvular grafts have shown that this approach enables in situ regeneration of pulmonary valves with long-term functionality in vivo. However, the evolution and mechanisms of inflammation, polymer absorption and tissue regeneration are largely unknown, and adverse valve remodeling and intra- and inter-valvular variability have been reported. Therefore, the goal of the present study was to gain a mechanistic understanding of the in vivo regenerative processes by combining routine histology and immunohistochemistry, using a comprehensive sheep-specific antibody panel, with Raman microspectroscopy for the spatiotemporal analysis of in situ tissue-engineered pulmonary valves with follow-up to 24 months from a previous preclinical study in sheep. The analyses revealed a strong spatial heterogeneity in the influx of inflammatory cells, graft resorption, and foreign body giant cells. Collagen maturation occurred predominantly between 6 and 12 months after implantation, which was accompanied by a progressive switch to a more quiescent phenotype of infiltrating cells with properties of valvular interstitial cells. Variability among specimens in the extent of tissue remodeling was observed for follow-up times after 6 months. Taken together, these findings advance the understanding of key events and mechanisms in material-driven in situ heart valve tissue engineering. STATEMENT OF SIGNIFICANCE: This study describes for the first time the long-term in vivo inflammatory and regenerative processes that underly in situ heart valve tissue engineering using resorbable synthetic scaffolds. Using a unique combinatorial analysis of immunohistochemistry and Raman microspectroscopy, important spatiotemporal variability in graft resorption and tissue formation was pinpointed in in situ tissue-engineered heart valves, with a follow-up time of up to 24 months in sheep. This variability was correlated to heterogenous regional cellular repopulation, most likely instigated by region-specific differences in surrounding tissue and hemodynamics. The findings of this research contribute to the mechanistic understanding of in situ tissue engineering using resorbable synthetics, which is necessary to enable rational design of improved grafts, and ensure safe and robust clinical translation.

[Organoids for the advancement of intraoperative diagnostic procedures]. / Organoide zur Weiterentwicklung der intraoperativen Diagnostik.

In the context of cancer surgery, there is always a trade-off between oncological safety and preservation of function. This is especially true in pelvic surgery due to the close relationship to the pelvic floor muscles, blood supply and nerves. Currently, risk models, preoperative imaging, the surgeon's assessment, and the intraoperative frozen section serve as the basis for decision-making. New imaging techniques and standardization in frozen section have significantly improved this in recent years. However, limitations remain due to time delays as well as more difficult correct anatomical assignment in the follow-up. Alternative intraoperative techniques may overcome this limitation in the future. Patient-derived organoids have emerged as an important new research vehicle in recent years. They are based on tumor stem cells that, under special culture conditions, form three-dimensional replicas of the original tissue. This makes them ideally suited for testing individual system therapies but also as a validation technique for new intraoperative diagnostic procedures. The Research Training Group 2543/I, which is funded by the German Research Foundation, is researching the potential of new diagnostic methods in an interdisciplinary team regarding validation in addition to intraoperative frozen sections.

Elastin-like hydrogel stimulates angiogenesis in a severe model of critical limb ischemia (CLI): An insight into the glyco-host response.

Critical limb ischemia (CLI) is characterized by the impairment of microcirculation, necrosis and inflammation of the muscular tissue. Although the role of glycans in mediating inflammation has been reported, changes in the glycosylation following muscle ischemia remains poorly understood. Here, a murine CLI model was used to show the increase of high mannose, α-(2, 6)-sialic acid and the decrease of hybrid and bisected N-glycans as glycosylation associated with the ischemic environment. Using this model, the efficacy of an elastin-like recombinamers (ELR) hydrogel was assessed. The hydrogel modulates key angiogenic signaling pathways, resulting in capillary formation, and ECM remodeling. Arterioles formation, reduction of fibrosis and anti-inflammatory macrophage polarization wa also induced by the hydrogel administration. Modulation of glycosylation was observed, suggesting, in particular, a role for mannosylation and sialylation in the mediation of tissue repair. Our study elucidates the angiogenic potential of the ELR hydrogel for CLI applications and identifies glycosylation alterations as potential new therapeutic targets.

Hyaluronic acid as a macromolecular crowding agent for production of cell-derived matrices.

Cell-derived matrices (CDMs) provide an exogenous source of human extracellular matrix (ECM), with applications as cell delivery vehicles, substrate coatings for cell attachment and differentiation, and as biomaterial scaffolds. However, commercial application of CDMs has been hindered due to the prolonged culture time required for sufficient ECM accumulation. One approach to increasing matrix deposition in vitro is macromolecular crowding (MMC), which is a biophysical phenomenon that limits the diffusion of ECM precursor proteins, resulting in increased ECM accumulation at the cell layer. Hyaluronic acid (HA), a natural MMC highly expressed in vivo during fetal development, has been shown to play a role in ECM production, but has not been investigated as a macromolecule for increasing cell-mediated ECM deposition in vitro. In the current study, we hypothesized that HA can act as a MMC, and increase cell-mediated ECM production. Human dermal fibroblasts were cultured for 3, 7, or 14 days with 0%, 0.05%, or 0.5% high molecular weight HA. Ficoll 70/400 was used as a positive control. SDS-PAGE, Sircol, and hydroxyproline assays indicated that 0.05% HA-treated cultures had significantly higher mean collagen deposition at 14 days, whereas Ficoll 70/400-treated cultures had significantly lower collagen production compared to the HA and untreated controls. However, fluorescent immunostaining of ECM proteins and quantification of mean gray values did not indicate statistically significant differences in ECM production in HA or Ficoll 70/400-treated cultures compared to untreated controls. Raman imaging (a marker-free spectral imaging method) indicated that HA increased ECM deposition in human dermal fibroblasts. These results are consistent with decreases in CDM stiffness observed in Ficoll 70/400-treated cultures by atomic force microscopy. Overall, these results indicate that there are macromolecule- and cell type- dependent effects on matrix assembly, turnover, and stiffness in cell-derived matrices. STATEMENT OF SIGNIFICANCE: Cell-derived matrices (CDMs) are versatile biomaterials with many regenerative medicine applications, including as cell and drug delivery vehicles and scaffolds for wound healing and tissue regeneration. While CDMs have several advantages, their commercialization has been limited due to the prolonged culture time required to achieve CDM synthesis in vitro. In this study, we explored the use of hyaluronic acid (HA) as a macromolecular crowder in human fibroblast cell cultures to support production of CDM biomaterials. Successful application of macromolecular crowding will allow development of human cell-derived, xeno-free biomaterials that re-capitulate the native human tissue microenvironment.

Controlled and tuneable drug release from electrospun fibers and a non-invasive approach for cytotoxicity testing.

Electrospinning is an attractive method to generate drug releasing systems. In this work, we encapsulated the cell death-inducing drug Diclofenac (DCF) in an electrospun poly-L-lactide (PLA) scaffold. The scaffold offers a system for a sustained and controlled delivery of the cytotoxic DCF over time making it clinically favourable by achieving a prolonged therapeutic effect. We exposed human dermal fibroblasts (HDFs) to the drug-eluting scaffold and employed multiphoton microscopy and fluorescence lifetime imaging microscopy. These methods were suitable for non-invasive and marker-independent assessment of the cytotoxic effects. Released DCF induced changes in cell morphology and glycolytic activity. Furthermore, we showed that drug release can be influenced by adding dimethyl sulfoxide as a co-solvent for electrospinning. Interestingly, without affecting the drug diffusion mechanism, the resulting PLA scaffolds showed altered fibre morphology and enhanced initial DCF burst release. The here described model could represent an interesting way to control the diffusion of encapsulated bio-active molecules and test them using a marker-independent, non-invasive approach.

Influence of aflibercept on platelet activation profile.

Aflibercept appears to accumulate in systemic circulation following intravitreal injections in therapy of neovascular age-related macular degeneration. This gives raise to the question of whether aflibercept affects platelets and their function such as activation and aggregation, which are substantial in the pathogenesis of an arterial thromboembolic event (ATE). In order to determine the effect of aflibercept in platelet activation, platelets from healthy volunteers were treated with aflibercept and its solvents at equal concentrations (0.04 µg/mL - 4 µg/mL - 40 µg/mL - 400 µg/mL - 4 mg/mL) for 10 and 30 min before addition of agonists. IgG1 antibody was used as a control. The surface expression of GPIIb/IIIa, P-selectin, and platelet-bound stromal-cell-derived factor-1, which are potential blood biomarkers for ATEs, was determined on resting and activated platelets by the multispectral imaging flow cytometry, combining the features of flow cytometry with fluorescence microscopy. Platelet aggregation was assessed with light transmission aggregometry. To determine whether aflibercept directly interacts with platelets, aflibercept was labeled with the fluorescence FITC. Co-treatment of platelets with thrombin or PAR-4-AP and aflibercept resulted in increased activation of the fibrinogen receptor GPIIb/IIIa in comparison to controls (P < 0.05). Interestingly, the expression of platelet-derived P-selectin and SDF-1 was not affected by aflibercept, except thrombin-activated CD62P with 0.04 µg/mL aflibercept (aflibercept vs. its solvent: MSI = 1.54, IC = 1.201-1.879 vs. MSI = 1.37, IC = 1.136-1.604 [P = 0.031]) and SDF-1 with 4 mg/mL aflibercept (aflibercept vs. its solvent: MSI = 1.971, IC = 1.206-2.737 vs. MSI = 1.200, IC = 0.738-1.662 [P = 0.041]). Although the levels of platelet-bound aflibercept-FITC were significantly increased in all activated platelets, no effect was observed in platelet aggregation. Albeit no impact of aflibercept was found on platelet aggregation under the studied experimental conditions, the increased activation of the fibrinogen receptor GPIIb/IIIa and the presence of a direct interaction between aflibercept and platelets may partially explain the risk of ATE in patients under aflibercept treatment due to FcγRIIa mediated αIIbß3 outside-in integrin signaling and transport of aflibercept into platelets. Therefore, the Fc domain seems to be involved in interactions between aflibercept and platelets. Further research is needed to explain the role of Fc containing aflibercept in the pathogenesis of drug-associated vascular events involving platelets, coagulation cascade, extracellular matrix proteins and other cells.

Visualizing tropoelastin in a long-term human elastic fibre cell culture model.

Elastin is an essential protein found in a variety of tissues where resilience and flexibility are needed, such as the skin and the heart. When aiming to engineer suitable implants, elastic fibres are needed to allow adequate tissue renewal. However, the visualization of human elastogenesis remains in the dark. To date, the visualization of human tropoelastin (TE) production in a human cell context and its fibre assembly under live cell conditions has not been achieved. Here, we present a long-term cell culture model of human dermal fibroblasts expressing fluorescence-labelled human TE. We employed a lentiviral system to stably overexpress Citrine-labelled TE to build a fluorescent fibre network. Using immunofluorescence, we confirmed the functionality of the Citrine-tagged TE. Furthermore, we visualized the fibre assembly over the course of several days using confocal microscopy. Applying super resolution microscopy, we were able to investigate the inner structure of the elastin-fibrillin-1 fibre network. Future investigations will allow the tracking of TE produced under various conditions. In tissue engineering applications the fluorescent fibre network can be visualized under various conditions or it serves as a tool for investigating fibre degradation processes in disease-in-a-dish-models.

Loss of spatial organization and destruction of the pericellular matrix in early osteoarthritis in vivo and in a novel in vitro methodology.

OBJECTIVES: Current repair procedures for articular cartilage (AC) cannot restore the tissue's original form and function because neither changes in its architectural blueprint throughout life nor the respective biological understanding is fully available. We asked whether two unique elements of human cartilage architecture, the chondrocyte-surrounding pericellular matrix (PCM) and the superficial chondrocyte spatial organization (SCSO) beneath the articular surface (AS) are congenital, stable or dynamic throughout life. We hypothesized that inducing chondrocyte proliferation in vitro impairs organization and PCM and induces an advanced osteoarthritis (OA)-like structural phenotype of human cartilage. METHODS: We recorded propidium-iodine-stained fetal and adult cartilage explants, arranged stages of organization into a sequence, and created a lifetime-summarizing SCSO model. To replicate the OA-associated dynamics revealed by our model, and to test our hypothesis, we transduced specifically early OA-explants with hFGF-2 for inducing proliferation. The PCM was examined using immuno- and auto-fluorescence, multiphoton second-harmonic-generation (SHG), and scanning electron microscopy (SEM). RESULTS: Spatial organization evolved from fetal homogeneity, peaked with adult string-like arrangements, but was completely lost in OA. Loss of organization included PCM perforation (local micro-fibrillar collagen intensity decrease) and destruction [regional collagen type VI (CollVI) signal weakness or absence]. Importantly, both loss of organization and PCM destruction were successfully recapitulated in FGF-2-transduced explants. CONCLUSION: Induced proliferation of spatially characterized early OA-chondrocytes within standardized explants recapitulated the full range of loss of SCSO and PCM destruction, introducing a novel in vitro methodology. This methodology induces a structural phenotype of human cartilage that is similar to advanced OA and potentially of significance and utility.

Raman spectroscopy as an analytical tool for melanoma research.

BACKGROUND: Raman spectroscopy is an optical noninvasive screening technology that generates individual fingerprints of living cells by reflecting their molecular constitution. AIM: To discriminate melanoma cells from melanocytes, to identify drug-induced melanoma cell death stages (apoptosis, necrosis, autophagy) and to assess the susceptibility of melanoma cells to anticancer therapy. METHODS: We used Raman spectroscopy on normal and melanoma cells, and on wild-type (WT) and mutant melanoma cells, to investigate whether the technique could distinguish between different types of cells, identify mutations and evaluate response to anticancer therapy. RESULTS: Using the multivariate principal component analysis of the Raman spectra, melanocytes could be distinguished from melanoma cells, and WT melanoma cells could be distinguished from melanoma cells with BRAF or NRAS mutations. When we used the apoptosis inducer staurosporine, the necrosis inducer 3-bromopyruvate and the autophagy inducer resveratrol to induce cell death in SKMEL28 melanoma cells, Raman spectroscopy clearly distinguished between these three types of cell death, as confirmed by immunoblotting. Finally, the technique could discriminate between different melanoma cell lines according to their susceptibility to high-dose ascorbate. CONCLUSIONS: Raman spectroscopy is a powerful noninvasive tool to distinguish between melanocytes and melanoma cells, to analyze the specific type of cell death in melanoma cells, and to predict the susceptibility of melanoma cells to anticancer drugs.

Prevention of device-related tissue damage during percutaneous deployment of tissue-engineered heart valves.

BACKGROUND: Endovascular application of pulmonary heart valves has been recently introduced clinically. A tissue-engineering approach was pursued to overcome the current limitations of bovine jugular vein valves (degeneration and limited longevity). However, deployment of the delicate tissue-engineered valves resulted in severe tissue damage. Therefore the objective of this study was to prevent tissue damage during the folding and deployment maneuver. MATERIAL AND METHODS: Porcine pulmonary heart valves, small intestinal submucosa, and ovine carotid arteries were obtained from a slaughterhouse. After dissection and antimicrobial incubation, the valves were trimmed (removal of sinus and most of the muscular ring) to fit into the deployment catheter. The inside (in-stent group, n = 6) or outside (out-stent group, n = 6) of a nitinol stent was covered by an acellular small intestinal submucosa, and the valves were sutured into the stent. The valves were folded, tested for placement in the deployment catheter, and decellularized enzymatically. Myofibroblasts were obtained from carotid artery segments and seeded onto the scaffolds. The seeded constructs were placed in a dynamic bioreactor system and cultured for 16 consecutive days. After endothelial cell seeding, the constructs were folded, deployed, and processed for histology and surface electron microscopy. RESULTS: The valves opened and closed competently throughout the entire dynamic culture. Surface electron microscopy revealed an almost completely preserved tissue in the in-stent group. Stents covered with small intestinal submucosa on the outside, however, showed severe damage. CONCLUSION: This study demonstrates that small intestinal submucosa covering of the inside of a pulmonary valved stent can prevent stent strut-related tissue damage.

Multiphoton autofluorescence imaging of intratissue elastic fibers.

Multiphoton induced blue/green autofluorescence by near infrared femtosecond laser pulses has been used to selectively image intratissue elastic fibers in native and tissue engineered (TE) viable heart valves without any invasive tissue removal, embedding, fixation, and staining. Elastic fibers could be clearly distinguished from collagenous structures which emit ultraviolet/violet radiation when excited with intense ultrashort pulses due to second harmonic generation. Deep-tissue three-dimensional imaging of elastic fibers with submicron spatial resolution was performed by optical sectioning of heart valves using a multiphoton laser scanning microscope in connection with a tunable 80 MHz femtosecond laser source. The technology was used to diagnose extracellular matrix structures and cell resettlement of TE heart valves prior implantation. This novel non-invasive method opens the general possibility of high-resolution in situ imaging of elastic fibers, collagen structures and intracellular organelles in living intact tissues without staining.

Comparative study of cellular and extracellular matrix composition of native and tissue engineered heart valves.

Tissue engineering of heart valves utilizes biodegradable or metabolizable scaffolds for remodeling by seeded autologous cells. The aim of this study was to determine and compare extracellular matrix (ECM) formations, cellular phenotypes and cell location of native and tissue engineered (TE) valve leaflets. Ovine carotid arteries, ovine and porcine hearts were obtained from slaughterhouses. Cells were isolated from carotid arteries and dissected ovine, porcine and TE leaflets. TE constructs were fabricated from decellularized porcine pulmonary valves, seeded ovine arterial cells and subsequent 16 days dynamic in vitro culture using a pulsatile bioreactor. Native and TE valves were studied by histology (hematoxylin-eosin, resorcin-fuchsin, Movat pentachrome), NIR femtosecond multiphoton laser scanning microscopy and scanning electron microscopy (SEM). Cells of native and TE tissues were identified and localized by immunohistochemistry. Arterial, valvular and re-isolated TE-construct cells were processed for immunocytochemistry and Western blotting. ECM analysis and SEM revealed characteristical and comparable structures in native and TE leaflets. Most cells in native leaflets stained strongly positive for vimentin. Cells positive to alpha-smooth muscle actin (alpha-SMA), myosin and calponin were only found at the ventricular (inflow) side of ovine aortic and porcine pulmonary valve leaflets. Cells from TE constructs had a strong expression of vimentin, alpha-SMA, myosin, calponin and h-caldesmon throughout the entire leaflet. Comparable ECM formation and endothelial cell lining of native and TE leaflets could be demonstrated. However, immunostaining revealed significant differences between valvular cell phenotypes of native and TE leaflets. These results may be essential for further cardiovascular tissue engineering efforts.

ProteinChip system technology: a powerful tool to analyze expression differences in tissue-engineered blood vessels.

At the time of implantation, tissue-engineered constructs should resemble native tissues as closely as possible. At present, histology and biochemical methods are commonly used to compare tissue-engineered constructs with native tissue. A ProteinChip system based on surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI) has been developed that allows visualization of complex protein profiles from biological samples. The aim of this study was to determine whether the ProteinChip system is a suitable tool with which to compare the protein expression profiles of tissue-engineered aortic blood vessels with native tissues. Tissue-engineered blood vessel substitutes were fabricated with poly-4-hydroxybutyrate scaffolds, ovine vascular cell seeding, and dynamic tissue culture conditions. Engineered, ovine aortic, and carotid tissues were homogenized and total protein was extracted. Samples were analyzed on ProteinChip arrays. Analysis yielded reproducible protein profiles from all samples. About 150 distinct protein peaks were detected. Comparative analysis with ProteinChip software revealed that the protein profiles from native aorta and native carotid arteries were similar whereas early tissue-engineered samples displayed more distinct deviations. In conclusion, ProteinChip system technology is rapid, reproducible, and highly sensitive in highlighting differentially expressed proteins in tissue-engineered blood vessel substitutes.

Tissue engineering of ovine aortic blood vessel substitutes using applied shear stress and enzymatically derived vascular smooth muscle cells.

Compared to native blood vessels, all clinically available blood vessel substitutes perform suboptimally. Numerous approaches to tissue engineer (TE) blood vessels have been pursued using different scaffold materials, cell types, and culture conditions. Several limitations however remain to be overcome prior to the potential application in the arterial system. This study aimed at tissue engineering viable ovine blood vessels suitable for implantation into the systemic circulation of sheep. In recent studies vascular smooth muscle cells (vSMC) were derived by an explant technique. However, in this study we show that homogenous populations of differentiated vSMC were only obtained by enzymatic dispersion as characterized by immunostaining for specific vSMC marker proteins. In contrast the explant method yielded predominantly less differentiated myofibroblast-like cells. Enzymatically derived vSMC were seeded onto P-4-HB scaffolds and incubated either in a pulsatile flow bioreactor or under static conditions. Dynamically cultured TE blood vessel substitutes showed confluent layered tissue formation and were completely water resistant. They displayed significantly increased ECM synthesis, DNA, and protein content as well as vSMC marker expression. Mechanical properties of bioreactor cultured TE blood vessels approached those of native aorta. In conclusion ovine, aortic blood vessel substitutes were successfully created using enzymatically derived vSMC, bioabsorbable scaffolds, and applied shear stress.

Complete dynamic repopulation of decellularized heart valves by application of defined physical signals-an in vitro study.

OBJECTIVE: Cardiovascular tissue engineering is a novel concept to develop ideal heart valve substitutes. The objective of this study was to use decellularized porcine pulmonary valves, ovine cells and dynamic tissue culture to obtain viable and biomechanically stable constructs, resembling native aortic heart valves. METHODS: Endothelial cells and myofibroblasts were obtained from ovine carotid arteries. Porcine pulmonary valves were decellularized enzymatically, reseeded and cultured using a hydrodynamic bioreactor system over a time period of 9 or 16 days. Controls were grown over an equivalent time period under static conditions. Specimens of each valve were examined biochemically (cell proliferation, DNA, collagen, 4-hydroxyproline, elastin and glycosaminoglycans), histologically (hematoxylin-eosin, Movat-pentachrome and immunostains) and mechanically (radial and circumferential strength). RESULTS: Histology and biochemical assays demonstrated the removal of almost all cells after decellularization with preservation of the extracellular matrix. Recellularization under pulsatile conditions was significantly improved after 9 and 16 days compared to static conditions. Biochemical and mechanical analysis revealed a continuous increase of cell mass, collagen and elastin contents and strength under pulsatile culture conditions compared to significantly lower values in the static controls. CONCLUSION: This study demonstrated the superiority of the hydrodynamic approach of cellular reseeding to replace decellularized porcine heart valves with ovine cells with almost complete preservation of extracellular matrix integrity.

Impact of decellularization of xenogeneic tissue on extracellular matrix integrity for tissue engineering of heart valves.

The multidisciplinary research of tissue engineering utilizes biodegradable or decellularized scaffolds with autologous cell seeding. Objective of this study was to investigate the impact of different decellularization protocols on extracellular matrix integrity of xenogeneic tissue by means of multiphoton femtosecond laser scanning microscopy, biochemical and histological analysis. Pulmonary valves were dissected from porcine hearts and placed in a solution of trypsin-EDTA and incubated at 37 degrees C for either 5, 8, or 24 h, followed by a 24 h PBS washing. Native and decellularized valves were processed for histology, DNA, cell proliferation, matrix proteins and biomechanical testing. Multiphoton NIR laser microscopy has been applied for high-resolution 3D imaging of collagen and elastin. Distinct differences in several ECM components following decellularization time were observed. Total GAG contents decreased in a time-dependent manner, with o-sulfated GAGs being more susceptible to degradation than n-sulfated GAGs. Efficiency of insoluble collagen extraction increased proportionally with decellularization time, suggesting ECM-integrity may be compromised with prolonged incubation. Biomechanical testing revealed a gradual weakening of mechanical strength with increased decellularization time. The enzymatic decellularization process of heart valves revealed a time-dependent loss of cells, ECM components and biomechanical strength. In order to avoid any immune response a thorough decellularization of 24 h remains mandatory.