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Biomedical subjects

Torsten Blunk

Publications and source records attributed to Torsten Blunk.

18 recordsLinked to original sources

Mechanistic insights into linear polyethylenimine-mediated gene transfer.

We recently debuted a variety of linear polyethylenimines (LPEIs) with low molecular weight as carriers for gene delivery. The highest transfection efficiency (approximately 44%) was obtained with LPEI 6.6 kDa, while the cytotoxicity remained low (approximately 90% of CHO-K1 cells survived the transfection procedure). Here, we investigated various steps during the transfection process using LPEI 8.1, 5.0 and 1.8 kDa, in order to gain a more complete insight into LPEI-mediated gene transfer and to explore conceptual aspects for further optimization. The cellular uptake characterized by flow cytometry was similar for LPEI 8.1 and 5.0 kDa, while it was significantly lower for LPEI 1.8 kDa. The transfection efficacy in contrast was at NP 24 20.07% for LPEI 8.1 kDa and 39.71% for LPEI 5.0 kDa. This suggests that the endocytosis seems not to be a decisive parameter that determines the efficacy of a polymer in the transfection process. Real-time PCR investigations revealed that LPEI 1.8 kDa likewise or even better protected plasmid from degradation compared to LPEI 5.0 or 8.1 kDa. Furthermore, we found that 1/6 to 1/3 intact plasmid DNA reached the intracellular compartments after complexation with LPEI 1.8 kDa. Therefore, the amount of plasmid DNA available in the cytoplasm seems not to be a limiting factor in the transfection process. That LPEI 8.1-polyplexes built at NP 12 in glucose and transfected in serum-free culture conditions were superior to those built in sodium chloride or transfected in serum-containing conditions points at the structure as a decisive parameter deserving more attention in future studies.

Animals↗

Long-term stable fibrin gels for cartilage engineering.

It is essential that hydrogel scaffold systems maintain long-term shape stability and mechanical integrity for applications in cartilage tissue engineering. Within this study, we aimed at the improvement of a commercially available fibrin gel in order to develop a long-term stable fibrin gel and, subsequently, investigated the suitability of the optimized gel for in vitro cartilage engineering. Only fibrin gels with a final fibrinogen concentration of 25mg/ml or higher, a Ca(2+) concentration of 20mm and a pH between 6.8 and 9 were transparent and stable for three weeks, the duration of the experiment. In contrast, when preparing fibrin gels with concentrations out of these ranges, turbid gels were obtained that shrank and completely dissolved within a few weeks. In rheological characterization experiments, the optimized gels showed a broad linear viscoelastic region and withstood mechanical loadings of up to 10,000 Pa. Bovine chondrocytes suspended in the optimized fibrin gels proliferated well and produced the extracellular matrix (ECM) components glycosaminoglycans and collagen type II. When initially seeding 3 million cells or more per construct (5mm diameter, 2mm thick), after 5 weeks of culture, a coherent cartilaginous ECM was obtained that was homogenously distributed throughout the whole construct. The developed fibrin gels are suggested also for other tissue engineering applications in which long-term stable hydrogels appear desirable.

Animals↗

Development of a spray congealing process for the preparation of insulin-loaded lipid microparticles and characterization thereof.

A spray congealing process for the preparation of protein-loaded microparticles was developed. The influence of the process parameters atomization pressure and spraying temperature on particle size and process yield was investigated by experimental design. The employed spray congealing technique enabled the production of microparticles with yields ranging from 79% to 95% and median particle sizes (d(0.5)) from 182.2 to 315 microm. Insulin lipid microparticles could be prepared without any loss of insulin during the preparation process and the protein stability was not affected by the spray congealing process as investigated by HPLC-MS analysis. The stability of insulin encapsulated in lipid microparticles under release conditions over 28 days was assessed by investigating the residual insulin content. Starting after 3 days of release, a continuous increase of desamidoinsulin in the remaining particles of up to 7.5% after 28 days was observed. An additional degradation product was detected by HPLC and HPLC-MS analysis and identified as a covalent insulin dimer by MALDI-ToF. The microparticles did not show a burst release and testing the insulin lipid microparticles in a fibrin gel chondrocyte culture revealed that the released insulin was bioactive and had a significant effect on chondrocyte extracellular matrix production.

Cartilage↗

Micronization of insulin by high pressure homogenization.

PURPOSE: The aim of this study was to establish the high pressure homogenization of proteins in non-aqueous suspension as an alternative method for classical micronization strategies and to investigate the effect of high pressure on protein stability and bioactivity. METHODS: The influence of drug loading, homogenization pressure and cycles on particle size reduction was investigated by experimental design using a Box Behnken matrix with insulin as a model compound. Particle size measurements were performed by laser light scattering. Protein stability was investigated by HPLC and HPLC-MS analysis and the bioactivity of insulin was tested in a chondrocyte proliferation assay. For investigations into the effect of temperature on protein stability, insulin was micronized in molten lipid at 75 degrees C in one cycle at 1,000 bar. RESULTS: Within one homogenization cycle at 1,500 bar, the particle size of insulin could be reduced from 15.8 to 7.3 microm, six cycles resulted in a particle size of 3.7 microm d(0.5) (50% of the particles are smaller than the indicated value). Evaluation of the response surface diagram revealed that the homogenization pressure had the highest impact on micronization efficiency, followed by the number of homogenization cycles. Protein stability was maintained during the micronization process as well as bioactivity. Micronization at elevated temperature (75 degrees C) had no effect on protein stability. CONCLUSION: High pressure homogenization of protein suspensions can be used as an alternative method for the micronization of proteins without affecting protein stability or bioactivity.

Algorithms↗

Steroid hormones strongly support bovine articular cartilage integration in the absence of interleukin-1beta.

OBJECTIVE: Posttraumatic integration of articular cartilage at fracture sites is essential for mechanical stability of cartilage, and ruptured cartilage is a prerequisite for early osteoarthritis. This study was undertaken to investigate effects on articular cartilage integration mediated by steroid hormones, interleukin-1beta (IL-1beta), and combinations thereof. METHODS: Articular cartilage blocks were cultured in partial apposition for 2 weeks with ascorbic acid, testosterone, 17beta-estradiol, and dehydroepiandrosterone (DHEA), with or without IL-1beta. Mechanical integration was measured as adhesive strength, i.e., the maximum force at rupture of integrated cartilage blocks divided by the overlap area. Glycosaminoglycan content was used to study synthesized extracellular matrix. RESULTS: Culture in medium without supplements did not lead to integration (adhesive strength 0 kPa). With administration of ascorbic acid (100 microg/ml), the median adhesive strength was 49 kPa. In comparison with ascorbic acid alone, all steroid hormones induced a strong, concentration-dependent stimulation of integration (with maximum values observed with DHEA at 3 x 10(-5)M, testosterone at 10(-8)M, and 17beta-estradiol at 10(-11)M). For testosterone and 17beta-estradiol, this was also reflected by an increase of glycosaminoglycan content. Adhesive strength was increased with IL-1beta at 10 pg/ml, but not at 1 pg/ml or 100 pg/ml. In the presence of both IL-1beta and sex hormones, integration of articular cartilage was reduced. CONCLUSION: This is the first study to demonstrate that steroid hormones such as 17beta-estradiol, DHEA, and testosterone stimulate articular cartilage integration. This effect is abrogated by low concentrations of IL-1beta. In the absence of IL-1beta or after neutralization of IL-1beta, steroid hormones might be favorable adjuvant compounds to optimize cartilage integration.

Animals↗

Gene delivery with low molecular weight linear polyethylenimines.

BACKGROUND: Linear polyethylenimine (LPEI) with a molecular weight (MW) of 22 kDa has been described as having a superior ability to induce gene transfer compared to its branched form. However, the transfection efficiency of the polymer cannot be enhanced beyond a certain limit due to cytotoxicity. We explored the potential of utilizing LPEIs with MWs ranging from 1.0 to 9.5 kDa to overcome this limitation. METHODS: Polyplexes of plasmid DNA encoding for the enhanced green fluorescent protein (EGFP) and various LPEIs were compared concerning their transfection efficiency and cytotoxicity in CHO-K1 and HeLa cells by flow cytometry. The involvement of endolysosomes in LPEI-mediated gene transfer was investigated by applying the proton pump inhibitor bafilomycin A1 and the lysosomotropic agent sucrose. Confocal laser scanning microscopy was applied to assess the size and shape of polyplexes under cell culture conditions, to detect their endolysosomal localization and to observe their translocation to the nucleus. RESULTS: The transfection efficiency could be altered by varying the MW and the amount of the polymer available for polyplex formation. The highest transfection efficiency (about 44%), i.e. the fraction of EGFP-positive cells, was obtained with LPEI 5.6 kDa, while the cytotoxicity remained low. The colocalization of polyplexes and endolysosomes was observed, and it appeared that the larger polyplexes escaped from the acidic organelles particularly quickly. For LPEI 5.0 and 9.0 kDa, the number of cells and nuclei that had taken up DNA after 6 hours was similar, as determined by flow cytometry. CONCLUSIONS: Our study suggests that LPEIs with low MWs are promising candidates for non-viral gene delivery, because they are more efficient and substantially less toxic than their higher MW counterparts.

Animals↗

Basic fibroblast growth factor enhances PPARgamma ligand-induced adipogenesis of mesenchymal stem cells.

Mesenchymal stem cells (MSCs) are capable of differentiating into a variety of lineages, including bone, cartilage, or fat, depending on the inducing stimuli and specific growth and differentiation factors. It is widely acknowledged that basic fibroblast growth factor (bFGF) modulates chondrogenic and osteogenic differentiation of MSCs, but thorough investigations of its effects on adipogenic differentiation are lacking. In this study, we demonstrate on the cellular and molecular level that supplementation of bFGF in different phases of cell culture leads to a strong enhancement of adipogenesis of MSCs, as induced by an adipogenic hormonal cocktail. In cultures receiving bFGF, mRNA expression of peroxisome proliferator-activated receptor gamma2 (PPARgamma2), a key transcription factor in adipogenesis, was upregulated even prior to adipogenic induction. In order to investigate the effects of bFGF on PPARgamma ligand-induced adipogenic differentiation, the thiazolidinedione troglitazone was administered as a single adipogenic inducer. Basic FGF was demonstrated to also strongly increase adipogenesis induced by troglitazone, that is, bFGF clearly increased the responsiveness of MSCs to a PPARgamma ligand.

Adipocytes↗

Generation of mature fat pads in vitro and in vivo utilizing 3-D long-term culture of 3T3-L1 preadipocytes.

Tissue-inherent factors such as cell-cell and cell-extracellular matrix interactions are regarded to exert a potentially large impact on adipogenesis as well as on secretory functions of adipose tissue. However, an appropriate 3-D adipogenesis model useful for addressing such interactions is still lacking. In this study, using tissue-engineering techniques, we demonstrate for the first time the development of coherent fat pads consisting of unilocular signet-ring cells in vitro. The constructs were generated by differentiating 3T3-L1 preadipocytes on 3-D polymeric scaffolds for either 9, 21, or 35 days in vitro. Only long-term culture yielded uniform tissues histologically comparable to native fat. Light and scanning electron microscopy provided direct evidence of 3-D tissue coherence and cell-cell contact in a tissue context, which was in strong contrast to conventional 2-D monolayer culture. Further differences between the two culture systems included enhanced secretion of leptin in 3-D tissue culture and differences in laminin expression (mRNA and protein level). Increase of triglyceride content over culture time and mRNA expression of other adipocyte genes, such as PPARgamma and Glut-4, were found to be similar. Implantation of long-term differentiated tissue constructs in nude mice resulted in further development and maintenance of fat pads. The presented model system is suggested to contribute to a better understanding of adipose tissue development and function facilitating studies on tissue-inherent interactions in vitro and in vivo.

3T3-L1 Cells↗

Polyplexes of polyethylenimine and per-N-methylated polyethylenimine-cytotoxicity and transfection efficiency.

For non-viral gene delivery, the carriers for DNA transfer into cells must be vastly improved. The branched cationic polymer polyethylenimine has been described as an efficient gene carrier. However, polyethylenimine was demonstrated to mediate substantial cytotoxicity. Therefore, this study is aimed at investigating per-N-methylated polyethylenimine, which is thought to have a much lower cytotoxicity due to its lower charge density. Results from a gel retardation assay and laser light scattering indicated that per-N-methylated polyethylenimine condenses DNA into small and compact nanoparticles with a mean diameter <150 nm. Furthermore, polyplexes of polyethylenimine and per-N-methylated polyethylenimine with DNA had a positive zeta potential and the polymers protected DNA from nuclease-mediated digestion. The transfection efficiency of polyethylenimine and per-N-methylated polyethylenimine was tested in CHO-K1 cells. Using green fluorescent protein as reporter gene and flow cytometry analysis, we demonstrated that per-N-methylated polyethylenimine has a lower cytotoxicity, but also a significantly lower transfection efficiency. Using propidium iodide staining, we could additionally distinguish between viable and dead cells. At NP > or = 12, per-N-methylated polyethylenimine showed a much higher cell viability and the ratio of viable and transfected cells to dead and transfected cells was about 1.5 to 1.7 fold higher than for polyethylenimine. The results of cell viability from flow cytometry analysis were confirmed by the MTS assay. Using luciferase reporter gene for transfection experiments, the gene expression of per-N-methylated polyethylenimine was lower at NP 6, 12 and 18 as compared to polyethylenimine, but at NP 24 it yielded similar levels.

Animals↗

Towards biomimetic scaffolds: anhydrous scaffold fabrication from biodegradable amine-reactive diblock copolymers.

The development of biomimetic materials and their processing into three-dimensional cell carrying scaffolds is one promising tissue engineering strategy to improve cell adhesion, growth and differentiation on polymeric constructs developing mature and viable tissue. This study was concerned with the fabrication of scaffolds made from amine-reactive diblock copolymers, N-succinimidyl tartrate monoamine poly(ethylene glycol)-block-poly(D,L-lactic acid), which are able to suppress unspecific protein adsorption and to covalently bind proteins or peptides. An appropriate technique for their processing had to be both anhydrous, to avoid hydrolysis of the active ester, and suitable for the generation of interconnected porous structures. Attempts to fabricate scaffolds utilizing hard paraffin microparticles as hexane-extractable porogens failed. Consequently, a technique was developed involving lipid microparticles, which served as biocompatible porogens on which the scaffold forming polymer was precipitated in the porogen extraction media (n-hexane). Porogen melting during the extraction and polymer precipitation step led to an interconnected network of pores. Suitable lipid mixtures and their melting points, extraction conditions (temperature and time) and a low-toxic polymer solvent system were determined for their use in processing diblock copolymers of different molecular weights (22 and 42 kDa) into highly porous off-the-shelf cell carriers ready for easy surface modification towards biomimetic scaffolds. Insulin was employed to demonstrate the principal of instant protein coupling to a prefabricated scaffold.

Biocompatible Materials↗

Determination of oxygen gradients in engineered tissue using a fluorescent sensor.

Nutrient and oxygen supply of cells are crucial to tissue engineering in general. If a sufficient supply cannot be maintained, the development of the tissue will slow down or even fail completely. Previous studies on oxygen supply have focused on measurement of oxygen partial pressures (pO(2)) in culture media or described the use of invasive techniques with spatially limited resolution. The experimental setup described here allows for continuous, noninvasive, high-resolution pO(2) measurements over the cross-section of cultivated tissues. Applying a recently developed technique for time-resolved pO(2) sensing using optical sensor foils, containing luminescent O(2)-sensitive indicator dyes, we were able to monitor and analyze gradients in the oxygen supply in a tissue over a 3-week culture period. Cylindrical tissue samples were immobilized on top of the sensors. By measuring the luminescence decay time, two-dimensional pO(2) distributions across the tissue section in contact with the foil surface were determined. We applied this technique to cartilage explants and to tissue-engineered cartilage. For both tissue types, changes were detected in monotonously decreasing gradients of pO(2) from the surface with high pO(2) to minimum pO(2) values in the center of the samples. Nearly anoxic conditions were observed in tissue constructs ( approximately 0 Torr) but not in excised cartilage discs ( approximately 20 Torr) after 1 day. Furthermore, the oxygen supply seemed to strongly depend on cell density and cell function. Additionally, histological analysis revealed a maximum depth of approximately 1.3 mm of regular cartilage development in constructs grown under the applied culture conditions. Correlating analytical and histological analysis with the oxygen distributions, we found that pO(2) values below 11 Torr might impair proper tissue development in the center. The results illustrate that the method developed is an ideal one to precisely assess the oxygen demand of cartilage cultures.

Animals↗

Differential effects of growth factors on tissue-engineered cartilage.

The effects of four regulatory factors on tissue-engineered cartilage were examined with specific focus on the ability to increase construct growth rate and concentrations of glycosaminoglycans (GAG) and collagen, the major extracellular matrix (ECM) components. Bovine calf articular chondrocytes were seeded onto biodegradable polyglycolic acid (PGA) scaffolds and cultured in medium with or without supplemental insulin-like growth factor (IGF-I), interleukin-4 (IL-4), transforming growth factor-beta1 (TGF-beta1) or platelet-derived growth factor (PDGF). IGF-I, IL-4, and TGF-beta1 increased construct wet weights by 1.5-2.9-fold over 4 weeks of culture and increased amounts of cartilaginous ECM components. IGF-I (10-300 ng/mL) maintained wet weight fractions of GAG in constructs seeded at high cell density and increased by up to fivefold GAG fractions in constructs seeded at lower cell density. TGF-beta1 (30 ng/mL) increased wet weight fractions of total collagen by up to 1.4-fold while maintaining a high fraction of type II collagen (79 plus minus 11% of the total collagen). IL-4 (1-100 ng/mL) minimized the thickness of the GAG-depleted region at the construct surfaces. PDGF (1-100 ng/mL) decreased construct growth rate and ECM fractions. Different regulatory factors thus elicit significantly different chondrogenic responses and can be used to selectively control the growth rate and improve the composition of engineered cartilage.

Animals↗

Effects of hedgehog proteins on tissue engineering of cartilage in vitro.

The effects of three derivatives of the N-terminal signaling domain of hedgehog proteins on cartilage engineered in vitro were investigated, with specific focus on the ability to increase tissue growth rate and concentrations of major extracellular matrix components, that is, glycosaminoglycans (GAG) and collagen, and on the effects on morphological appearance of the tissue. Bovine articular chondrocytes were cultured on biodegradable polyglycolic acid (PGA) scaffolds with or without the addition of dipalmitoylated sonic hedgehog (dp-shh), dipalmitoylated indian hedgehog (dp-ihh), or sonic hedgehog dimer (shh-dimer) to medium with either 1% or 10% fetal bovine serum (FBS). All three hedgehog proteins dose-dependently increased construct weights (by up to 1.95-fold, dp-shh at 1,000 ng/mL) and the fraction of GAG over 4 weeks (by up to 2.7-fold, dp-shh at 1,000 ng/mL), as compared to control constructs. Dp-shh and dp-ihh elicited similar responses; a 10-fold higher concentration of nonacylated shh-dimer was necessary to reach comparable results. Positive hedgehog effects were more pronounced in medium containing 1% FBS than in medium containing 10% FBS; however, at either FBS concentration, cartilaginous tissues grown in the presence of hedgehog proteins appeared morphologically more mature. Hedgehog derivatives thus appear as promising candidates to improve the development and composition of engineered cartilage.

Animals↗

Three-dimensional in vitro model of adipogenesis: comparison of culture conditions.

In vivo and in vitro studies have demonstrated both promise and current limitations in tissue engineering of fat. Herein, we report the establishment of a well-defined three-dimensional (3-D) in vitro model useful for systematic investigations of 3-D adipogenesis. Polyglycolic acid fiber meshes were dynamically seeded with 3T3-L1 preadipocytes; subsequently, cell-polymer constructs were hormonally induced and cultivation under three different conditions was evaluated. Regarding tissue coherence and intracellular lipid content, culture of cell-polymer constructs either dynamically in well plates or in stirred bioreactors yielded similar results, which were distinctly improved compared with static conditions in well plates. At the protein and mRNA levels, significantly increased expression of genes characteristic for a mature adipose phenotype was demonstrated for constructs dynamically cultured in well plates, as compared with static conditions. Furthermore, investigation of lipolysis under stimulating and inhibiting conditions demonstrated functionality of the dynamically differentiated constructs. Using dynamic culture conditions, the presented in vitro model system is suggested as a valuable tool serving both fat tissue engineering and basic research by facilitating investigations of tissue-inherent features not possible under conventional 2-D culture conditions.

3T3-L1 Cells↗

PEGylation does not impair insulin efficacy in three-dimensional cartilage culture: an investigation toward biomimetic polymers.

A major goal in tissue engineering is the controlled application of growth factors. As a novel application system, we are currently developing biomimetic polymers that are processed into three-dimensional scaffolds. Bioactive proteins will be covalently bound to the polymers via a poly(ethylene glycol) (PEG) linker. Of paramount importance is the maintenance of the biological activity of the protein after PEGylation and covalent binding to the polymer. Therefore, within this study, insulin used as a model protein was PEGylated with an active succinimidyl ester of poly(ethylene glycol) (SS-NH-PEG) (MW ~2000) and biological effects of the protein-PEG conjugate were monitored in comparison with unmodified insulin. No significant differences in chondrocyte proliferation were observed in a conventional proliferation assay after treatment with insulin or PEGylated insulin. In a complex three-dimensional cartilage-engineering model the effects of insulin and PEGylated insulin were investigated over a wide concentration range (0.025-25 microg/mL). Insulin and PEGylated insulin at equivalent concentrations resulted in cartilaginous tissue constructs exhibiting identical wet weight, cell number, biochemical composition of the extracellular matrix, and histological appearance, both compounds significantly improving tissue quality as compared with control constructs. In conclusion, the presented study demonstrates that PEGylation of insulin using SS-NH-PEG did not change the activity of the protein in a complex biological environment and is regarded as a step toward the development of biomimetic polymers.

Animals↗

Toward the development of biomimetic polymers by protein immobilization: PEGylation of insulin as a model reaction.

Many current tissue-engineering investigations aim at the rational control of cell adhesion and tailored composition of biomaterial surfaces by immobilizing various protein and peptide components, such as growth factors. As a step on the way to develop polymers that allow for such surface modifications, water-soluble polymers were used as model substances to examine reactions with proteins containing amine groups. Consequently, the uncommon PEGylation of insulin in aqueous buffers was used to characterize reaction products and simulate the intended immobilization step for surface modification. Amine reactive poly(ethylene glycol)s were synthesized and characterized by (1)H nuclear magnetic resonance and gel-permeation chromatography. Furthermore, the model protein insulin was characterized concerning its accessible amino groups, using a fluorescent dye (TAMRA-SE). The resulting reaction products were identified by reversed-phase high-performance liquid chromatography and electrospray mass spectrometry. After PEGylation with hydrolytically stable poly(ethylene glycol) succinimidyl ester, the obtained PEGylated insulin was investigated by gel filtration chromatography, indicating successful attachment of the hydrophilic polymer chains. Application of an aqueous PEGylation scheme opens the door to the immediate investigation of various growth factors in cell culture, allowing for direct assessment of biological activity after forming the polymer-protein constructs with regard to later immobilization on surfaces.

Animals↗

Adipose tissue engineering based on mesenchymal stem cells and basic fibroblast growth factor in vitro.

Despite the clinical need for reconstructive and plastic surgery, the supply of engineered adipose tissue equivalents still remains a challenge. As yet, only preadipocytes have been applied as a cell material for the in vitro tissue engineering of fat. Herein, we report the establishment of a three-dimensional (3-D) long-term cell culture, using bone marrow-derived mesenchymal stem cells (MSCs) as an alternative cell source and custom-made poly(lactic-co-glycolic acid) (PLGA) scaffolds as a cell carrier. Cell-polymer constructs were cultivated for 4 weeks in both the absence and presence of basic fibroblast growth factor (bFGF), which was previously shown to strongly enhance the adipogenesis of MSCs in conventional 2-D short-term culture. A striking enhancement of the adipogenic differentiation of MSCs and tissue development caused by bFGF in the 3-D culture was observed by osmium tetroxide histology and scanning electron microscopy. At the molecular level, reflecting the increased accumulation of lipids, bFGF increased the enzymatic activity of glycerol-3-phosphate dehydrogenase, a late marker of adipogenesis, and the expression of adipocyte-specific genes peroxisome proliferator activated receptor-gamma2 (PPARgamma2) and glucose transporter-4 (GLUT4), as assessed by reverse transcription-polymerase chain reaction. This study demonstrates that the use of bone marrow-derived MSCs, especially in combination with bFGF, may represent a promising approach to adipose tissue engineering.

Adipogenesis↗