Biological behaviour of an endothelial cell line (HPMEC) on vascular prostheses grafted with hydroxypropylgamma-cyclodextrine (HPgamma-CD) and hydroxypropylbeta-cyclodextrine (HPbeta-CD).

The cytocompatibility of cyclodextrins (CDs) grafting on vascular polyester (PET) prostheses for further loading with biomolecules was investigated in this study. Viability tests demonstrated no toxicity of HP-CDs and PolyHP-CDs at 4,000 mg/l with survival rates of 80 to 96%. Proliferation tests using the human pulmonary microvascular endothelial cell line (HPMEC-ST1) revealed an excellent biocompatibility for Melinex (Film form of PET). For Polythese and Polymaille, a good proliferation rate was observed at 3 days (60-80%) but decreased at 6 days (56-73%). For all CD-grafted samples, low proliferation rates were observed after 6 days (35-38%). Vitality tests revealed excellent functional capacities of HPMEC cells after 3 and 6 days for all samples. Adhesion kinetics tests showed a similar adhesion of HPMEC cells on control and Melinex. A low adhesion was observed on Polythese and especially on Polymaille compared to control. After CD grafting, the cell adhesion was decreased. The woven or knitted architecture and CD grafting were the most likely causes of this weak adhesion. The adhesion kinetic test was confirmed by SEM observations and immunocytochemistry. The low proliferation of HPMEC on virgin prostheses and especially on grafted prostheses was not due to a cytotoxic effect, but to the physical surface characteristics of the prostheses.

Experimental approaches to study vascularization in tissue engineering and biomaterial applications.

The success of tissue engineering and biomaterial applications is not only dependent on the growth and functioning of the organ- or tissue-specific cells on the biomaterial but is entirely dependent in most cases on a successful vascularization after implantation. The process of vascularization involves angiogenesis; the formation of new blood vessels which spread into the implant material and supply the existing cells with the nutrients to survive. We have established in vitro methods using human microvascular endothelial cells to evaluate novel biomaterials for endothelial cell attachment, cytotoxicity, growth, angiogenesis and the effects on gene regulation. These in vitro studies can be used to rapidly evaluate the potential success of a new biomaterial and for the development of matrix scaffolds which will promote a physiological vascularization response.

Endothelial accumulation of hydroxyethyl starch and functional consequences on leukocyte-endothelial interactions.

To date, accumulation of hydroxyethyl starch (HES) has been studied mainly in skin specimens, but there are no detailed reports available regarding starch accumulation in the endothelium. Because endothelial cells play an essential role during shock, we studied the accumulation of HES in human umbilical venous endothelial cells (HUVEC). HUVEC (n = 9) were incubated with a fluorescein-conjugated HES 200/0.5 (FITC-HES) at 0.5-20 mg/ml for 1-72 h. FITC-HES was internalized dose- and time-dependently by pinocytosis into secondary lysosomes. Asymptotic elimination curves showed that 50% of the formerly ingested molecules could not be eliminated. Despite accumulation, starch molecules did not attenuate the expression of E-selectin, ICAM-1 or VCAM-1 on TNF-alpha-activated HUVEC. However, apart from adhesion molecule expression, perfusion studies showed that HES reduced neutrophil adhesion by direct inhibition of integrin-mediated interactions.

Tissue response and biomaterial integration: the efficacy of in vitro methods.

Implantation involves tissue trauma, which evokes an inflammatory response, coupled to a wound healing reaction, involving angiogenesis, fibroblast activation and matrix remodelling. Until now the type and extent of such reactions to give optimal integration of various biomaterials are practically unknown. Three principal fields of research can yield useful data to understand these phenomena better: studies on explanted biomaterials, animal models and relevant in vitro techniques. This paper will present examples of the latter field and the application of endothelial cell (EC) culture systems to study the effects of important tissue (e.g. pro-inflammatory cytokines, chemokines) and material (e.g. metal ions, particulate debris) factors on the regulation of the inflammatory and angiogenic response. A central feature is the use of microvascular endothelial cells (MEC), which can be used in both 2-and 3-dimensional (3-D) assays. We have also used genetic manipulation to develop a permanent MEC line from the human lung (HPMEC-ST1), which is being tested for its suitability to study cell-biomaterial interactions. In addition, suitable in vitro techniques are being developed in order to investigate drug delivery systems (DDS). Of particular interest is the targeting of the central nervous system, our approach being to establish a human model of the blood-brain barrier (BBB). A mainstay of our scientific philosophy is that such in vitro methods can make an important contribution to understanding biological reactions at the tissue-biomaterial interface and thus further a causal approach to tissue engineering (TE) and drug delivery applications.

[Pathomechanisms of impaired wound healing by metallic corrosion products]. / Pathomechanismen der gestörten Wundheilung durch metallische Korrosionsprodukte.

BACKGROUND: Metallic materials of variable chemical composition have been used in dental practice for a long time. Complications with respect to tissue healing after insertion of implants are well documented. In this paper we present relevant aspects of the related fields of inflammation and repair processes and focus on the pathomechanisms of this impaired healing response. MODULATION OF WOUND HEALING: This latter process is modulated by specific metal ions released by corrosion activity as well as by wear particles, which influence the function of the participating cell types (e.g. endothelial cells). IN VITRO MODELS: In this context, in vitro models are presented that permit study of isolated aspects of the complex sequence of events at the biomaterial-tissue interface. Furthermore, newly developed, computer-assisted methods allowing an objective quantification of biomaterial/corrosion product-induced effects on complex processes, such as angiogenesis in vitro, are demonstrated. Because of the central importance of titanium implants in maxillofacial surgery, new experimental approaches to study possible negative effects are presented. Finally, the relevance of such studies for clinical implantology is evaluated.

Generation of human pulmonary microvascular endothelial cell lines.

The limited lifespan of human microvascular endothelial cells in cell culture represents a major obstacle for the study of microvascular pathobiology. To date, no endothelial cell line is available that demonstrates all of the fundamental characteristics of microvascular endothelial cells. We have generated endothelial cell lines from human pulmonary microvascular endothelial cells (HPMEC) isolated from adult donors. HPMEC were cotransfected with a plasmid encoding the catalytic component of telomerase (hTERT) and a plasmid encoding the simian virus 40 (SV40) large T antigen. Cells transfected with either plasmid alone had an extended lifespan, but the cultures eventually entered crisis after several months of proliferation. Only those cells that were transfected with both plasmids acquired the capacity to grow in vitro without demonstrating major crisis, and these cells have been in culture for 24 months. HPMEC isolated from two different donors were used, generating two populations of immortalized cells, HPMEC-ST1 and HPMEC-ST2. Single cell-derived clones of the immortalized cells HPMEC-ST1 exhibited growth characteristics that were similar to those of the parental HPMEC. One selected clone, HPMEC-ST1.6R, displayed all major constitutively expressed and inducible endothelial phenotypic markers, including platelet endothelial cell adhesion molecule (PECAM-1, CD31), von Willebrand factor (vWF), and the adhesion molecules, intercellular adhesion molecule (ICAM-1), vascular adhesion molecule (VCAM-1), and E-selectin. In addition, an angiogenic response was demonstrated by sprout formation on a biological extracellular matrix (Matrigel). The HPMEC-ST1.6R cells did not form tumors in nude mice. The microvascular endothelial cell line, HPMEC-ST1.6R, will be a valuable tool for the study of microvascular endothelial physiology and pathology including gene expression, angiogenesis, and tumorigenesis.

Comparative sequence analysis of the core- and NS5-region of hepatitis C virus from tumor and adjacent non-tumor tissue.

The sequence variability within the core- and non-structural 5 (NS5)-region of the hepatitis C virus (HCV) was investigated in tumor and non-tumor tissue of 8 patients with HCV-associated hepatocellular carcinoma (HCC). Analyses of multiple clones containing polymerase chain reaction-amplified HCV sequences revealed a significantly higher variability within the core-region of tumor tissue isolates than of isolates from non-tumor tissue. Mutant sequence diversity ranged from silent mutations, as well as amino acid substitutions, appearance of in frame stop codons and deletions leading to frame-shifts. In contrast, the variability of the NS5-region sequences between isolates from tumor and non-tumor tissue was not significantly different. These observations might have important implications on the pathology of HCV, especially its potential tumorigenicity.

Akv murine leukemia virus enhances bone tumorigenesis in hMT-c-fos-LTR transgenic mice.

hMt-c-fos-LTR transgenic mice (U. Rüther, D. Komitowski, F. R. Schubert, and E. F. Wagner. Oncogene 4, 861-865, 1989) developed bone sarcomas in 20% (3/15) of females at 448 +/- 25 days and in 8% (1/12) of males at 523 days. After infection of newborns with Akv, an infectious retrovirus derived from the ecotropic provirus of the AKR mouse, 69% (20/28) of female animals and 83% (24/29) of males developed malignant fibrous-osseous tumors. The tumors in infected transgenics developed with higher frequency and a 200-days shorter mean tumor latency period. The hMt-c-fos-LTR transgene was expressed in all the fibrous-osseous tumors. They also showed newly integrated Akv proviruses, but in most tumors Akv was detected and expressed in only a small number of the tumor cells. Wild-type C3H mice infected with Akv developed benign osteomas with an incidence of 33% and a latency period of 474 days. The data indicate that Akv exerts distinct pathogenic effects on the skeleton. In hMt-c-fos-LTR transgenic mice, predisposed to bone sarcomagenesis, Akv acts synergistically with the fos transgene, resulting in the development of fibrous-osseous tumors.

[Murine leukemia virus Akv promotes bone tumor development in fos-transgenic mice]. / Das murine Leukämievirus Akv wirkt als Promoter der Knochentumorentwicklung fos-transgener Mäuse.

Newborn hMT-fos-LTR transgenic C3H mice and their non-transgenic siblings were infected with Akv, derived from the ecotropic provirus of the AKR mouse. Bone sarcomas in non-infected transgenics were observed in 20% (3/15) of females at 448 +/- 25 days and in 8% (1/12) of males at 523 days. Akv-infected transgenics developed bone tumors with higher frequency and at younger age: Females in 69% (20/28) at 268 +/- 122 days, males in 83% (24/29) at 279 +/- 109 days. In the majority of the bone tumors of Akv-infected transgenics (70% in females, 59% in males) cellular atypia was lacking and the histological pattern resembled human parosteal osteosarcoma. Only 50% (12/24) of bone tumors in Akv-infected transgenics revealed newly integrated virus sequences by Southern analysis. PCR analysis detected Akv sequences in DNAs of all tumors. Obviously, the insertion of Akv in a few cells induced the considerably accelerated bone tumor growth.

Fate and biological activity of exogenous DNA sequences during serial transfections in NIH/3T3 cells.

The efficiency and accuracy of serial transfections in NIH/3T3 fibroblasts were investigated with two plasmids carrying a dominant gene. One plasmid carried the activated ras oncogene of human origin inducing morphological alteration and the oncogenic phenotype of NIH/3T3 cells. The second plasmid carried the bacterial neoR gene conferring resistance to the neomycine analogue G 418. We observed no correlation between the presence of biologically active DNAs in primary transfectants and the capacities of these DNAs to transmit the exogenous information in a second cycle of transfection. Cellular DNA of only two of 13 ras and only 1 of 3 neoR transformants could transform NIH/3T3 in a second cycle of transfections. About half of secondary transfectants, derived from those primary transfectants which did transmit the exogenous DNA, contained apparently complete exogenous sequences and transmitted it efficiently and even with the original site of integration in the host DNA in a third cycle of transfection. Exogenous DNA sequences were amplified in the majority of secondary transfectants but did not enhance biological activity in a third cycle of transfer. The exogenous DNA was found to undergo rearrangements in oncogenic transformants propagated in cell culture.

Leukaemia virus infection promotes fibroblast transformation by normal BALB/c mouse DNA.

All normal cells are thought to carry genetic information for oncogenic transformation, which, on activation to continuous expression, might make the cell cancerous. The presently known transforming retroviruses contain transforming genes which were probably derived by recombination of a slow oncogenic retrovirus with cellular sequences closely related to these genes. It was recently reported that cellular DNA fragments from normal tissue culture cells could transform mouse fibroblasts in vitro with a low efficiency. High efficiency of transformation was observed in secondary transfections only when high molecular weight DNA from transformed recipient cells was used as the transforming agent. We observed that DNA isolated from different BALB/c mouse organs can transform both NIH/3T3 and BALB/3T3 cells, although at a low frequency. In attempts to increase the initial efficiency of transformation, we have found that preinfection of recipient 3T3 cells with murine leukaemia viruses markedly enhances focus formation by normal BALB/c DNA fragments.