Biomedical subjects

Martin C Harmsen

Publications and source records attributed to Martin C Harmsen.

At least 19 recordsLinked to original sources

PubMed2006

Efficient differentiation of CD14+ monocytic cells into endothelial cells on degradable biomaterials.

Vascular tissue engineering aims at creating self-renewing, anti-thrombogenic, vascular grafts, which can be based on endothelial progenitor cells (EPC). EPC harbor essential features such as plasticity and longevity. Unfortunately, the archetype CD34(+) EPC is rare in peripheral blood. Monocytes, i.e. CD14(+) cells also have the ability to differentiate into endothelial-like cells and are by far more abundant in peripheral blood than are CD34(+) EPC. Therefore, CD14(+) cells would seem appropriate candidates for tissue engineering of small-diameter blood vessels. In this study, we investigated the differentiation of CD14(+) cells on three biodegradable biomaterials under angiogenic conditions. Morphological analyses, gene transcript analyses, endothelial marker (i.e. VE-Cadherin and eNOS) and macrophage marker (i.e. CD68 and CD163) expression analyses, revealed that a small fraction (15-25%) of cultured CD14(+) cells differentiated into macrophages after 21 days of culture. The majority of CD14(+) cells (>75%) differentiated into endothelial-like cells (ELC) on all biomaterials used. The expression of endothelial markers was similar to their expression on HUVEC. Since CD14(+) cells are present in high numbers in adult peripheral blood, easy to isolate and because they easily differentiate into ELC on biomaterials, we conclude that CD14(+) cells are a suitable cell source for progenitor-based vascular tissue engineering.

Biocompatible Materials↗

PubMed2006

Stem cell-related cardiac gene expression early after murine myocardial infarction.

OBJECTIVE: Clinical experimental stem cell therapy after myocardial infarction appears feasible, but its use has preceded the understanding of the working mechanism. The ischemic recipient cardiac environment is determinative for the attraction and subsequent fate of stem cells. Here, we studied expression levels of genes that are anticipated to be essential for adequate stem cell-based cardiac repair at various time-points during the 1 month period following myocardial infarction (MI). METHODS: Gene expression in the hearts of mice that underwent MI by permanent or transient (30 min) ligation of the coronary artery was monitored using quantitative RT-PCR analysis of mRNA isolated from whole heart sections as well as from specific, laser micro-dissected, regions of sections. Protein expression was performed by immunohistochemical stainings and Western blot analysis. RESULTS: Many inflammatory genes were highly expressed for at least 1 week after MI. The expression of pro-angiogenic genes such as bFGF, VEGF-A and VEGF-R2 changed only marginally post-MI. Markers used to test stem cell gene expression remained unchanged post-MI with the exception of G-CSF and GM-CSF, which are genes that are also known to enhance the inflammatory response. Analysis of micro-dissected regions revealed that SDF-1, SCF (both stem cell attractants) and VEGF-R2 (involved in angiogenesis) gene expression was slightly decreased especially in the infarcted region. CONCLUSION: Genes that are generally considered to participate in stem cell-related processes and angiogenesis were not upregulated after MI, whereas the inflammatory gene expression dominated. Modulation of this imbalance might be of value for stem cell-mediated therapy.

Animals↗

PubMed2006

Bone marrow-derived myofibroblasts contribute to the renal interstitial myofibroblast population and produce procollagen I after ischemia/reperfusion in rats.

Bone marrow-derived cells (BMDC) have been proposed to exert beneficial effects after renal ischemia/reperfusion injury (IRI) by engraftment in the tubular epithelium. However, BMDC can give rise to myofibroblasts and may contribute to fibrosis. BMDC contribution to the renal interstitial myofibroblast population in relation to fibrotic changes after IRI in rats was investigated. A model of unilateral renal IRI (45 min of ischemia) was used in F344 rats that were reconstituted with R26-human placental alkaline phosphatase transgenic BM to quantify BMDC contribution to the renal interstitial myofibroblast population over time. After IRI, transient increases in collagen III transcription and interstitial protein deposition were observed, peaking on days 7 and 28, respectively. Interstitial infiltrates of BMDC and myofibroblasts reached a maximum on day 7 and gradually decreased afterward. Over time, an average of 32% of all interstitial alpha-smooth muscle actin-positive myofibroblasts coexpressed R26-human placental alkaline phosphatase and, therefore, were derived from the BM. BMD myofibroblasts produced procollagen I protein and therefore were functional. The postischemic kidney environment was profibrotic, as demonstrated by increased transcription of TGF-beta and decreased transcription of bone morphogenic protein-7. TGF-beta protein was present predominantly in interstitial myofibroblasts but not in BMD myofibroblasts. In conclusion, functional BMD myofibroblasts infiltrate in the postischemic renal interstitium and are involved in extracellular matrix production.

Animals↗

PubMed2006

Chemical and biological properties of supramolecular polymer systems based on oligocaprolactones.

We show that materials with a diverse range of mechanical and biological properties can be obtained using a modular approach by simply mixing different ratios of oligocaprolactones that are either end-functionalized or chain-extended with quadruple hydrogen bonding ureido-pyrimidinone (UPy) moieties. The use of two UPy-synthons allows for easy synthesis of UPy-modified polymers resulting in high yields. Comparison of end-functionalized UPy-polymers with chain-extended UPy-polymers shows that these polymers behave distinctively different regarding their material and biological properties. The end-modified UPy-polymer is rather stiff and brittle due to its high crystallinity. Disks made of this material fractures after subcutaneous implantation. The material shows a low inflammatory response which is accompanied by the formation of a fibrous capsule, reflecting the inertness of the material. The chain-extended UPy-material on the contrary is practically free of crystalline domains and shows clear flexible properties. This material deforms after in-vivo implantation, accompanied with cellular infiltration. By mixing both polymers, materials with intermediate properties concerning their mechanical and biological behaviour can be obtained. Surprisingly, a 20:80 mixture of both polymers with the chain-extended UPy-polymer in excess shows flexible properties without visible deformation upon implantation for 42 days. This mixture, a blend formed by intimate mixing through UPy-UPy interaction, also shows a mild tissue response accompanied with the formation of a thin capsule. The material does not become more crystalline upon implantation. Hence, this mixture might be an ideal scaffold material for soft tissue engineering due to its flexibility and diminished fibrous tissue formation, and illustrates the strength of the modular approach.

Animals↗

PubMed2006

Circulating CD34+ progenitor cells modulate host angiogenesis and inflammation in vivo.

Within the phenotypically and functionally heterogeneous group of circulating progenitor cells (CPC), a subclass of cells with vascular repair potential have been identified. These CPC are detected and isolated based on single or combined expression of CD34, CD133 and VEGFR-2, and referred to as endothelial progenitor cells. Here we asked whether CPC subsets defined by single expression of these markers exhibit functional heterogeneity. As functional parameters, we chose the capacity of CPC to differentiate into endothelial cells. Moreover, we studied their role in remodeling by recruitment of inflammatory cells, an aspect that has been little explored. We established an in vivo model in which the intrinsic functional capacity of these human CPC subsets was studied. Human CD34+ CPC, but not CD133+ or VEGFR-2+ CPC, seeded in Matrigel pellets and transplanted subcutaneously in a nude mouse host, contributed little to donor-derived neovascularization. However, host angiogenesis in the Matrigel implant, as demonstrated by the presence of capillaries containing erythrocytes and expressing mouse CD31, was strong in response to implantation of human CD34+ CPC and significantly lower in response to the other two CPC subsets. Moreover, the CD34+ CPC subset was significantly superior to CD133+ CPC and VEGFR-2+ CPC in the recruitment of host monocytes/macrophages. These three CPC populations were further dissected into seven discrete subsets, based on three-parameter flow cytometry analysis of combined expression patterns of CD34, CD133 and VEGFR-2. In conclusion, in our system, CD34+ CPC contribute marginally to neovascularization by differentiation but are potent regulators of the host angiogenic and pro-inflammatory response, suggesting a possible role for these cells in the remodeling of vascular lesions.

AC133 Antigen↗

PubMed2006

CD64-directed immunotoxin inhibits arthritis in a novel CD64 transgenic rat model.

Macrophages are known to play a key role during inflammation in rheumatoid arthritis (RA). Inflammatory macrophages have increased expression of CD64, the high-affinity receptor for IgG. Targeting this receptor through a CD64-directed immunotoxin, composed of an Ab against CD64 and Ricin A, results in effective killing of inflammatory macrophages. In this study, we show elevated levels of CD64 on synovial macrophages in both synovial lining and synovial fluid in RA patients. The CD64-directed immunotoxin efficiently eliminates activated synovial macrophages in vitro, while leaving quiescent, low CD64-expressing macrophages unaffected. To examine whether killing of CD64 macrophages results in therapeutic effects in vivo, we established an adjuvant arthritis (AA) model in newly generated human CD64 (hCD64) transgenic rats. We demonstrate that hCD64 regulation in this transgenic rat model is similar as in humans. After AA induction, treatment with CD64-directed immunotoxin results in significant inhibition of disease activity. There is a direct correlation between immunotoxin treatment and decreased macrophage numbers, followed by diminished inflammation and bone erosion in paws of these hCD64 transgenic rats. These data support synovial macrophages to play a crucial role in joint inflammation in AA in rats and in human RA. Selective elimination of inflammatory macrophages through a CD64-directed immunotoxin may provide a novel approach for treatment of RA.

Animals↗

PubMed2006

Kinetics of US28 gene expression during active human cytomegalovirus infection in lung-transplant recipients.

Targeting viral proteins early during infection may limit exacerbation of human cytomegalovirus infection. The viral chemokine-receptor homologue US28 interferes with leukocyte trafficking and, possibly, viral replication. Because US28 molecules are abundant on the surface of infected cells, this homologue is a potential target for antiviral therapy. To assess the relationship between US28 and disease activity, we measured, by quantitative reverse-transcription polymerase chain reaction, the levels of US28 and immediate-early (IE) 1 gene transcripts in the blood of lung-transplant recipients. We found that, during primary and secondary infection, the IE1 and US28 genes have early transcription kinetics and are expressed at similar levels. This may render US28 an attractive target for antiviral therapy.

Adult↗

PubMed2006

The human cytomegalovirus-encoded receptor US28 increases the activity of the major immediate-early promoter/enhancer.

The activation of the major immediate-early promoter (MIEP) is a key event in the cytomegalovirus replication cycle and is dependent on cellular transcription factors which are partially activated by viral proteins. Expression of the viral chemokine receptor homolog US28 results in constitutive activation of pro-inflammatory transcription factors that may be involved in the activation of the major immediate-early promoter/enhancer. Using reporter gene assays in human embryonic kidney cells, we found that US28 signaling was responsible for increased major immediate-early promoter/enhancer activity which was independent of beta-chemokine binding. Inhibition of nuclear factor-kappaB (NF-kappaB) only partially blocked the effect of US28, whereas treatment with a specific p38 mitogen activated kinase (MAPK) inhibitor fully abrogated the US28-induced enhancement of promoter activity. Our results suggest that during human cytomegalovirus (HCMV) infection, US28 in epithelial cells transactivates the major immediate-early promoter/enhancer via the activation of p38 MAPK and downstream signaling that partially involves NF-kappaB.

Artificial Gene Fusion↗

PubMed2006

The correlation between difference in foreign body reaction between implant locations and cytokine and MMP expression.

The foreign body reaction (FBR) differs between subcutaneously and supra-epicardially implanted materials. We hypothesize that this is a result of differences in cytokine, chemokine and matrix metalloproteinase (MMP) dynamics. Therefore we applied collagen disks subcutaneously and on the epicardium in mice and analyzed the FBR from day 1 to 21. Both the influx of leukocytes and implant degradation were higher in supra-epicardially implanted collagen than in subcutaneously implanted material. This correlated with a higher gene expression of pro-inflammatory cytokines such as IL-1 and IL-6, and a lower expression of the anti-inflammatory cytokine IL-10. Furthermore, the higher supra-epicardial expression of PMN attractants CXCL1/KC and CXCL2/MIP2 correlated with a higher and prolonged PMN influx. The gene expression levels of collagen degrading MMPs, i.e. MMP8, MMP13 and MMP14 were similar in subcutaneous and supra-epicardial disks. However, the activity of these enzymes was markedly higher supra-epicardially. In addition, the MMP9 expression was higher supra-epicardially, suggesting a role for this enzyme in the degradation process. In conclusion, a strong pro-inflammatory milieu is generated after supra-epicardial implantation that enables prolonged PMN presence and activation. This, together with the high supra-epicardial MMP9 level, could explain the observed difference in Col-I degradation between locations.

Animals↗

PubMed2006

Molecular recognition in poly(epsilon-caprolactone)-based thermoplastic elastomers.

The molecular recognition properties of the hydrogen bonding segments in biodegradable thermoplastic elastomers were explored, aiming at the further functionalization of these potentially interesting biomaterials. A poly(epsilon-caprolactone)-based poly(urea) 2 was synthesized and characterized in terms of mechanical properties, processibility and histocompatibility. Comparison of the data with those obtained from the structurally related poly(urethane urea) 1 revealed that the difference in hard segment structure does not significantly affect the potency for application as a biomaterial. Nevertheless, the small differences in hard block composition had a strong effect on the molecular recognition properties of the hydrogen bonding segments. High selectivity was found for poly(urea) 2 in which bisureidobutylene-functionalized azobenzene dye 3 was selectively incorporated while bisureidopentylene-functionalized azobenzene dye 4 was completely released. In contrast, the incorporation of both dyes in poly(urethane urea) 1 led in both cases to their gradual release in time. Thermal analysis of the polymers in combination with variable temperature infrared experiments indicated that the hard blocks in 1 showed a sharp melting point, whereas those in 2 showed a very broad melting trajectory. This suggests a more precise organization of the hydrogen bonding segments in the hard blocks of poly(urea) 2 compared to poly(urethane urea) 1 and explains the results from the molecular recognition experiments. Preliminary results revealed that a bisureidobutylene-functionalized GRGDS peptide showed more supramolecular interaction with the PCL-based poly(urea), containing the bisureidobutylene recognition unit, as compared to HMW PCL, lacking this recognition unit.

3T3 Cells↗

PubMed2006

Cellular and molecular dynamics in the foreign body reaction.

Intracorporally implanted materials, such as medical devices, will provoke the body to initiate an inflammatory reaction. This inflammatory reaction to implanted materials is known as the foreign body reaction (FBR) and is characterized by 3 distinct phases: onset, progression, and resolution. The FBR proceeds in the creation of a dynamic microenvironment that is spatially well organized. The progression of the FBR is regulated by soluble mediators, such as cytokines, chemokines, and matrix metalloproteinases (MMPs), which are produced locally by tissue cells and infiltrated inflammatory cells. These soluble mediators orchestrate the cascade of cellular processes in the microenvironment that accompanies the FBR, consisting of cellular activation, angiogenesis, extravasation, migration, phagocytosis, and, finally, fibrosis. The nature of the FBR requires that the soluble mediators act in a spatial and temporally regulated manner as well. This regulation is well known for several inflammatory processes, but scarce knowledge exists about the intricate relationship between the FBR and the expression of soluble mediators. This review discusses the key processes during the initiation, progression, and resolution phase, with emphasis on the role of soluble mediators. Besides other sites of implantation, we focus on the subcutaneous implantation model.

Animals↗

PubMed2005

The enzymatic degradation of scaffolds and their replacement by vascularized extracellular matrix in the murine myocardium.

Replacement of injured myocardium by cell-based degradable scaffolds is a novel approach to regenerate myocardium. Understanding the foreign body reaction (FBR) induced by the scaffold is requisite to predict unwanted site effects or implant failure. We evaluated the FBR against a biodegradable scaffold applied on injured myocardium in mice. Cryolesions and collagen type I scaffolds (Col-I) were applied to the left ventricle of mice. Cell infiltration, neovascularization, collagen deposition, matrix metalloproteinase (MMP-8) expression, enzymatic activity and scaffold degradation were determined at different time points (2-70 days). Infiltration of mainly macrophages, neutrophils and blood vessels was completed within 14 days. High numbers of neutrophils accumulated around the Col-I fibers and degradation of Col-I fibers into small fragments was observed on day 14. Active MMP-8 co-localized with the neutrophils on day 14, indicating enzymatic degradation of Col-I by neutrophil collagenase. Highly vascularized extracellular matrix remained at day 70. No differences were observed in the FBR to Col-I after application on healthy or injured myocardium. The FBR had no adverse effects on the adjacent myocardial tissue. In conclusion, cardiac scaffolds are degraded by MMP-8 and replaced by vascularized extracellular matrix during the FBR on injured myocardium.

Animals↗

PubMed2005

A modular and supramolecular approach to bioactive scaffolds for tissue engineering.

Bioactive polymeric scaffolds are a prerequisite for the ultimate formation of functional tissues. Here, we show that supramolecular polymers based on quadruple hydrogen bonding ureido-pyrimidinone (UPy) moieties are eminently suitable for producing such bioactive materials owing to their low-temperature processability, favourable degradation and biocompatible behaviour. Particularly, the reversible nature of the hydrogen bonds allows for a modular approach to gaining control over cellular behaviour and activity both in vitro and in vivo. Bioactive materials are obtained by simply mixing UPy-functionalized polymers with UPy-modified biomolecules. Low-molecular-weight bis-UPy-oligocaprolactones with cell adhesion promoting UPy-Gly-Arg-Gly-Asp-Ser (UPy-GRGDS) and the synergistic UPy-Pro-His-Ser-Arg-Asn (UPy-PHSRN) peptide sequences are synthesized and studied. The in vitro results indicate strong and specific cell binding of fibroblasts to the UPy-functionalized bioactive materials containing both UPy-peptides. An even more striking effect is seen in vivo where the formation of single giant cells at the interface between bioactive material and tissue is triggered.

3T3 Cells↗

PubMed2005

Viral chemokine-modulatory proteins: tools and targets.

The chemokine network is an extensive system that regulates many immune functions such as leukocyte locomotion, T cell differentiation, angiogenesis and mast cell degranulation. Tight control of chemokines is vital for proper immune function. Not surprisingly, viruses have found ways to subvert or exploit the immune system in order to persist in co-existence with their hosts. Several viral immune evasion genes encode proteins that modulate the chemokine network. We attempt to identify which aspects of the chemokine control mechanisms are susceptible to modulation. Chemokine-glycosaminoglycan interaction, extracellular processing of chemokines and chemokine scavenging will be discussed in the light of poxvirus and herpesvirus immune evasion. Viral chemokine-modulatory proteins may either be targets for anti-viral therapy or lead the way to new anti-inflammatory chemokine-modulating drugs.

Anti-Inflammatory Agents↗

PubMed2005

The modulation of angiogenesis in the foreign body response by the poxviral protein M-T7.

The foreign body response is characterized by enhanced recruitment of inflammatory cells. As the directional movement of cells is controlled by chemokines, disruption of the chemokine network would be an attractive approach to improve biocompatibility of an implanted material. The sequestration of chemokines by cell surface-expressed glycosaminoglycans (GAGs) is vital for in vivo chemokine activity. The myxoma virus encodes a soluble protein, M-T7, that interacts with conserved GAG-binding domains of chemokines to block chemokine-mediated leukocyte recruitment. We hypothesized that M-T7 might also affect the function of other inflammation-associated proteins in addition to chemokines that bind to GAG. In our studies, we focussed on the modulation of the GAG-binding molecules macrophage chemoattractant protein-1 (MCP-1) and vascular endothelial growth factor-164 (VEGF164) in the inflammatory reaction against subcutaneously implanted degradable cross-linked dermal sheep collagen discs in AO rats. Genetic delivery of M-T7 delays the influx of macrophages into the collagen discs. In addition, angiogenesis around the implanted material was reduced. The discs revealed reduced levels of rat MCP-1 and rat VEGF164. This was not due to down regulation of transcription of the genes that encode MCP-1 and VEGF164. Our in vivo observations suggest that, in addition to chemokines such as MCP-1, M-T7 neutralizes VEGF164.

Animals↗

PubMed2005

Protease activity of plasma hemopexin.

BACKGROUND: Previous studies into the relevance of a putative circulating factor in the pathogenesis of minimal change nephrotic syndrome have opened the possibility that plasma hemopexin might be an important effector molecule in this disorder. Thus, intra renal infusion of isolated plasma hemopexin into rats induced minimal change like glomerular lesions and proteinuria. Both, in vivo and in vitro effects of the active isoform of hemopexin could be attributed to protease activity of this molecule. However, the question remained whether hemopexin per se rather than some contaminating plasma factor is responsible for the potential enzymatic activity of this molecule. METHODS: Recombinant hemopexin was prepared according to standard methods in Pichia pastoris and compared for its identity and protease activity with plasma hemopexin using Western blotting and various in vitro assays. Unilateral renal perfusion in anesthetized rats was used to test the proteinuria inducing capacity of recombinant hemopexin versus heat-inactivated recombinant hemopexin. RESULTS: The blotting results show identical 85 kD bands in both native as well as recombinant hemopexin. Incubation of kidney tissue with recombinant hemopexin resulted in loss of of glomerular ectoapyrase and sialoglycoproteins, as shown by immunohistochemistry, which effect can be inhibited with the serine protease inhibitor phenylmethanesulfonyl fluoride. Artificial substrates for serine proteases, like kallikrein or thrombin, are hydrolysed by recombinant hemopexin in vitro, and not by heat-inactivated recombinant hemopexin or saline. Unilateral kidney perfusion of recombinant hemopexin, in contrast to control Pichia transfection products or heat-inactivated recombinant hemopexin, followed by a protein marker showed significantly enhanced urinary protein leakage 5.0, 10.0, and 15.0 minutes after perfusion. CONCLUSION: It is concluded that the hemopexin molecule as such can potentially act as a toxic protease, leading in the rat to proteinuria and glomerular alterations characteristic for minimal change nephrotic syndrome.

Animals↗

PubMed2005

Determinants of tubular bone marrow-derived cell engraftment after renal ischemia/reperfusion in rats.

BACKGROUND: Ischemia/reperfusion (I/R) injury is a major cause of acute renal failure (ARF). ARF is reversible, due to an innate regenerative process, which is thought to depend partly on bone marrow-derived progenitor cells. The significance of these cells in the repair process has been questioned in view of their relatively low frequency. Here, we hypothesize that the severity of renal damage and the postischemic recovery time are determinants of tubular bone marrow-derived cell (BMDC) engraftment. METHODS: We used a model of unilateral renal I/R in F344 rats reconstituted with R26-human placental alkaline phosphatase (hPAP) transgenic bone marrow, in which we quantified and characterized tubular BMDC engraftment with increasing severity of damage and in time. RESULTS: After I/R injury, BMDC engrafted the tubular epithelium and acquired an epithelial phenotype. Tubular epithelial BMDC engraftment increased with longer ischemic time, indicating that tubular epithelial BMDC engraftment increases with the severity of damage. The number of circulating progenitor cells doubled early after I/R injury and was followed by a transient increase in tubular epithelial BMDC engraftment. The latter positively correlated with morphological recovery of the kidney over time. CONCLUSION. The extent of tubular BMDC engraftment depends on the severity of renal damage and follows a distinct time course after I/R injury. Therefore, the severity of damage and time course need to be taken into account when interpreting data on the role of tubular BMDC engraftment in renal repair after I/R injury.

Acute Kidney Injury↗

PubMed2004

Inhibition of cytomegalovirus infection by lactoferrin in vitro and in vivo.

Lactoferrin is an antimicrobial agent, that, amongst other viruses, inhibits cytomegalovirus (CMV). In this study, we addressed the mechanism(s) by which lactoferrin interacts with CMV and its target cells to inhibit infection. We also studied the antiviral activity of lactoferrin in vivo in rat CMV models with and without immune suppression. We cationized a protein of similar molecular weight, i.e. human serum albumin (HSA), as well as a protein with a smaller molecular weight (beta-lactoglobulin). While HSA itself displayed no anti-CMV activity in vitro, cationic HSA inhibited CMV replication to a similar extent as lactoferrin. Time-of-addition assays indicated that all cationic proteins interacted with an early event in the infection and pre-incubation of cells rather than of virus significantly reduced CMV replication. Rats were treated with lactoferrin (4, 40 or 160 mg/kg, intravenously), beginning at 6h after CMV administration. Subsequently, the rats were treated three times a week. As a positive control, CMV-infected rats were treated with cidofovir, and this agent proved to be highly active in the rat models for CMV. Treatment with lactoferrin was beneficial when infection was initiated with cell-free virus, but not with virus-infected leukocytes. Lactoferrin treatment led to a 10-fold reduction in the final virus titers (salivary glands) at 4 weeks after infection in the immunocompromised rats. Lactoferrin exerted its effects via inhibition of cell entry rather than via stimulation of the immune system.

Animals↗