Biomedical subjects

H Gerhardt

Publications and source records attributed to H Gerhardt.

At least 19 recordsLinked to original sources

PubMed2006

Heparan sulphate requirement in platelet-derived growth factor B-mediated pericyte recruitment.

HS (heparan sulphate) plays a key role in angiogenesis, by interacting with growth factors required in the process. It has been proposed that HS controls the diffusion, and thus the availability, of platelet-derived growth factor B that is needed for pericyte recruitment around newly formed capillaries. The present paper summarizes our studies on the importance of HS structure in this regulatory process.

Animals↗

PubMed2001

Lack of pericytes leads to endothelial hyperplasia and abnormal vascular morphogenesis.

The association of pericytes (PCs) to newly formed blood vessels has been suggested to regulate endothelial cell (EC) proliferation, survival, migration, differentiation, and vascular branching. Here, we addressed these issues using PDGF-B-- and PDGF receptor-beta (PDGFR-beta)--deficient mice as in vivo models of brain angiogenesis in the absence of PCs. Quantitative morphological analysis showed that these mutants have normal microvessel density, length, and number of branch points. However, absence of PCs correlates with endothelial hyperplasia, increased capillary diameter, abnormal EC shape and ultrastructure, changed cellular distribution of certain junctional proteins, and morphological signs of increased transendothelial permeability. Brain endothelial hyperplasia was observed already at embryonic day (E) 11.5 and persisted throughout development. From E 13.5, vascular endothelial growth factor-A (VEGF-A) and other genes responsive to metabolic stress became upregulated, suggesting that the abnormal microvessel architecture has systemic metabolic consequences. VEGF-A upregulation correlated temporally with the occurrence of vascular abnormalities in the placenta and dilation of the heart. Thus, although PC deficiency appears to have direct effects on EC number before E 13.5, the subsequent increased VEGF-A levels may further abrogate microvessel architecture, promote vascular permeability, and contribute to formation of the edematous phenotype observed in late gestation PDGF-B and PDGFR-beta knock out embryos.

Animals↗

PubMed2001

[Therapy of active Crohn disease with Boswellia serrata extract H 15].

BACKGROUND: The purpose of this clinical trial was to compare efficacy and safety of the Boswellia serrata extract H15 with mesalazine for the treatment of active Crohn's disease. PATIENTS AND METHODS: Randomised, double-blind, verum-controlled, parallel group comparison for which 102 Patients were randomised. The per protocol population included 44 patients treated with H15 and 39 patients treated with mesalazine. As primary outcome measure the change of the Crohn Disease Activity Index (CDAI) between the status of enrolment and end of therapy was chosen. H 15 was tested on non-inferiority compared to standard treatment with mesalazine. RESULTS: The CDAI between the status of enrolment and end of therapy after treatment with H15 was reduced by 90 and after therapy with mesalazine by 53 scores in the mean. In this non-inferiority-trial the test hypothesis was confirmed by the statistical analysis. The difference between both treatments could not be proven to be statistically significant in favor to H15 for the primary outcome measure. The secondary efficacy endpoints confirm the assessment of the comparison of H15 and mesalazine. The proven tolerability of H15 completes the results of the shown clinical efficacy. CONCLUSIONS: The study confirms that therapy with H15 is not inferior to mesalazine. This can be interpreted as evidence for the efficacy of H15 according to the state of art in the treatment of active Crohn's disease with Boswellia serrata extract, since the efficacy of mesalazine for this indication has been approved by the health authorities. Considering both safety and efficacy of Boswellia serrata extract H15 it appears to be superior over mesalazine in terms of a benefit-risk-evaluation.

Adult↗

PubMed2000

Localization of Legionella bacteria within ribosome-studded phagosomes is not restricted to Legionella pneumophila.

In this report, we investigate the intracellular fate of selected members of the genus Legionella within the monocytic cell line Mono Mac 6 cells. By means of electron microscopy and immunocytochemistry, we could show that Legionella pneumophila as well as Legionella longbeachae are able to induce ribosome-studded phagosomes which associate with the rough endoplasmic reticulum (RER), whereas Legionella micdadei remains to be located within smooth phagosomes but also shows signs of RER association. In addition, we could demonstrate a remarkable correlation between the phagosome type and the morphological phenotype of intracellular bacteria: within ribosome-studded phagosomes, bacteria generally lacked the outer coat of low electron density whereas bacteria within the smooth phagosomes still possessed this outer coat. The virulence factors responsible for inhibition of phagosome maturation and their distribution within the genus Legionella as well as the biological significance of the morphological difference of bacteria within smooth and ER-associated phagosomes remain to be investigated.

Endoplasmic Reticulum↗

PubMed2000

The peripapillary glia of the optic nerve head in the chicken retina.

The eye of reptiles and birds is characterized by an avascular retina and a vascular convolute called conus papillaris in reptiles and pecten oculi in birds which arises from the papilla nervi optici (PNO) or optic nerve head into the vitreous. At least in birds, this central part of the retina is the site of a heterogeneous population of glial cells. Müller cells reside in the retina, astrocytes in the optic nerve, and pecteneal glial cells in the pecten. The latter are developmentally related to the pigment epithelial cells. In addition to these established types of cells, there is a population of glial cells lining the base of the pecten oculi. In the present study, we investigated both the morphology and the development of these glial cells of the PNO in a series of chicken embryos. These cells were called peripapillary glial cells. They were characterized by their morphology and by their spatiotemporal expression of antigens typical of glial cells (intermediate filaments and glutamine synthetase). They reside at the border between the retina and the optic nerve and at the innermost border of the ventricular cleft representing transitional forms among Müller cells, astrocytes, and pigment epithelial cells. The developmental data suggest a migration of the perikarya of the peripapillary glia in vitread direction, which may coincide with that of the pecteneal glia. Whereas the pecteneal glial cells differentiate morphologically from E16 on, the peripapillary glia retain characteristics of radial glia by spanning the distance from the vitreous to the ventricular cleft. Blood vessels only occurred in the optic nerve head and the pecten oculi. No capillaries were found in the retinal tissue, beyond the peripapillary glia, leading us to suggest that these cells may play a role in demarcating the outer limit of vascularization. The functional properties of these cells are unknown but were discussed to include prevention of vessel growth into the avascular retina and/or axonal guidance during development.

Animals↗

PubMed2000

Differential expression of endothelial beta-catenin and plakoglobin during development and maturation of the blood-brain and blood-retina barrier in the chicken.

The development of the blood-brain barrier depends upon the formation of a closely regulated system of adherens and tight junctions. A prerequisite for a functional junction system is the linkage of transmembrane adhesion receptors (cadherins) to the cytoskeleton via catenins. The localization of specific catenins at the adherens junction correlates with the stability of interendothelial contacts in vitro, but in vivo data are lacking thus far. Investigating brain angiogenesis in the chicken, we demonstrated that beta-catenin, but not plakoglobin, initially codistributed with N-cadherin at the ablumenal endothelial membrane at contact sites to perivascular cells, from where both antigens disappeared during blood-brain barrier maturation. In contrast, plakoglobin was most prominent at the interendothelial junction where only small amounts of beta-catenin were present. Western-blot analysis revealed a stronger developmental decrease of beta-catenin than plakoglobin, whereas N-cadherin was completely lost. beta-Catenin but not N-cadherin was reinduced in brain endothelial cells during dedifferentiation in vitro and localized to the interendothelial junctions. These first in vivo data support the hypothesis that endothelial beta-catenin and N-cadherin are transiently relevant for the contact of brain endothelial to perivascular cells. Plakoglobin seems not to interact with N-cadherin but is exclusively localized at interendothelial junctions providing evidence for its role in the formation of stable adherens junctions, which may play a role for the initiation, and/or stabilization of tight junctions. Dev Dyn 2000;217:86-98.

Animals↗

PubMed2000

N-cadherin mediates pericytic-endothelial interaction during brain angiogenesis in the chicken.

Recruitment and adhesion of pericytes to endothelial cells represents a critical step in angiogenesis. We previously demonstrated the expression of neural (N)-cadherin at contact zones between pericytes and endothelial cells in embryonic chicken brain. To elucidate N-cadherin function in early angionenesis, we injected functionally blocking antibodies on embryonic days 4 and 5 into the tectal ventricle of chicken embryos. Brains were morphologically and immunocytochemically investigated on embryonic day 6. Blocking N-cadherin function resulted in defective pericyte adhesion, increased pericyte recruitment and disturbed vascular morphogenesis. Increased pericyte recruitment did not involve elevated pericytic proliferation. Concomitant disruption of ependymal adherens junctions and of endothelial-pericytic adhesion resulted in massive hemorrhaging in the basal forebrain, in misdirected endothelial sprouting, and ectopic vascularization. Morphological investigation of control embryos on embryonic days 4 and 5 indicated the initial involvement of pericytes in stabilization of angiogenic capillary sprouts. Together these results suggest that N-cadherin mediates adhesion, recognition, and signaling between pericytes and endothelial cells required for normal vascular morphogenesis.

Actins↗

PubMed2000

Legionella species of different human prevalence induce different rates of apoptosis in human monocytic cells.

Legionella species of different human prevalence were examined with respect to induction of apoptosis in the human monocytic cell line Mono Mac 6 (MM6). L. pneumophila serogroup 1 (Pontiac), L. pneumophila serogroup 1 (Philadelphia-1), L. longbeachae serogroup 1, L. gormanii, L. micdadei and L. steigerwaltii were used to infect MM6 cells. Subsequent induction of apoptosis was investigated by enzyme-linked immunosorbent assay (ELISA), gel electrophoresis of cellular DNA extracts, and staining of cells with the DNA dye 4', 6-diamidino-2-phenylindole (DAPI). Additionally, the concomitant occurrence of infection and apoptosis was demonstrated by a combination of immunohistochemistry with nuclear DAPI counterstaining. Induction of apoptosis in MM6 cells by a given species of the genus Legionella correlates with their human prevalence rather than with their ability to multiply within this human monocytic cell line. Furthermore, we found that initiation of apoptosis of Mono Mac 6 cells was dependent on direct adherence of the pathogenic bacteria to the host cell and was triggered by extracellular bacteria.

Apoptosis↗

PubMed2000

R- and B-cadherin expression defines subpopulations of glial cells involved in axonal guidance in the optic nerve head of the chicken.

Glial cells play a crucial role in the organization and function of the nervous system. Cell-cell adhesion receptors of the cadherin family have been shown to participate in distinct morphogenetic processes throughout the development of the CNS, but little is known about glial expression of cadherins. Applying immunofluorescence and confocal laser scanning microscopy, we investigated R- and B-cadherin expression in relation to the glial cell differentiation in the optic nerve head and pecten oculi of developing chicken. Throughout embryonic development, R- and B-cadherin were expressed in distinct cell populations, which differentiated into distinct subtypes of glial cells. R-cadherin was located in the glia limitans perivascularis et superficialis of the optic nerve and in cells bordering the optic nerve head, where it comes in contact with the retina. B-cadherin was located in the glia limitans perivascularis et superficialis of the pecten oculi and in a subset of cells at the retinal border. R-cadherin-expressing cells differentiated unequivocally into a glial fibrillary acidic protein (GFAP)-positive but glutamine synthetase (GS)-negative phenotype, whereas B-cadherin-expressing glia developed into a GS-positive but GFAP-negative phenotype. In addition, the B-cadherin-positive population developed into a highly pigmented cell type, which was consistently associated with pecten-type capillaries. By contrast, the R-cadherin-positive glia remained unpigmented and surrounded normal brain-phenotype capillaries. These data suggest that glial cells, like neurons, may use the expression of different cadherins to segregate and differentiate into distinct subtypes, which goes hand in hand with their involvement in special functions and morphogenetic processes. To address this issue, we selectively lysed both glial subtypes in developing embryos by microinjection of R- and B-cadherin antibodies with complement. First evidence is presented for R-cadherin-positive glial cells as crucial to the organization of the optic nerve and axonal guidance at its lateral margin. B-cadherin-positive cells are involved in the axonal guidance at the pecteneal margin, avoiding the ingrowth of axons into the pecten.

Animals↗

PubMed1999

Differentiation of a unique macroglial cell type in the pecten oculi of the chicken.

Glial cells in the CNS of vertebrates serve specialized functions in close interaction with surrounding neurons and blood vessels. In the avian eye, the neural tissue (retina) and the supporting vascular structure (pecten oculi) are spatially separated and comprise distinct glial cell types, i.e., the Müller glia and the pecteneal glia, respectively. In the present study we combined morphological and immunocytochemical investigations on the differentiation of the pecteneal glia in comparison to the retinal Müller glia, the retinal pigment epithelium, and the astrocytic cells of the optic nerve head in order to elucidate the nature, origin, and function of the pecteneal glia. Conventional transmission electron microscopy and freeze-fracture imaging revealed striking similarities between the pecteneal glia and retinal pigment epithelial cells at the transition zone to the optic nerve head. Immunofluorescence investigation identified specific labeling for vimentin and glutamine synthetase (GS) but not for glial fibrillary acidic protein (GFAP) in the mature pecteneal glia. Immunogold labeling confirmed the cellular specificity. GS labeling was weak during embryonic development but increasingly strong after hatching. Surprisingly, the intraneuroectodermal endothelial cells were highly immunopositive for GS throughout embryonic development and lost GS expression after hatching. GS expression in the pecteneal glia may participate in pH-regulation of the avian eye. Endothelial GS expression in the developing CNS may detoxify detrimental ammonium concentrations resulting from egg yolk degradation.

Animals↗

PubMed1999

Ultrastructural localization of adhesion molecules in the healthy and inflamed choroid plexus of the mouse.

The functional expression of vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1) and MAdCAM-1 in the choroid plexus is indicative of a role of this structure in the communication of the immune system with the central nervous system (CNS). In order to gain further insight into the possible functions of adhesion molecules expressed in the choroid plexus, we investigated the exact ultrastructural localization of VCAM-1, ICAM-1 and MAdCAM-1 on semithin and ultrathin cryosections of the choroid plexus of healthy mice and of mice suffering from experimental autoimmune encephalomyelitis (EAE). In the healthy choroid plexus VCAM-1 and ICAM-1, but not MAdCAM-1, could be detected on the apical surface of the choroid plexus epithelial cells. During EAE, immunoreactivity for VCAM-1 and ICAM-1 was dramatically increased. Additionally, apical expression of MAdCAM-1 was observed on individual choroid plexus epithelial cells during EAE. At the same time, VCAM-1, ICAM-1 or MAdCAM-1 were never present on the endothelial cells of the fenestrated capillaries within the choroid plexus. The polar expression of VCAM-1, ICAM-1 and MAdCAM-1 on the apical surface of choroid plexus epithelial cells, which form the blood-cerebrospinal fluid barrier, implies a previously unappreciated function of this barrier in the immunosurveillance of the CNS.

Animals↗

PubMed1999

The pecten oculi of the chicken: a model system for vascular differentiation and barrier maturation.

The pecten oculi is a convolute of blood vessels in the vitreous body of the avian eye. This structure is well known for more than a century, but its functions are still a matter of controversies. One of these functions must be the formation of a blood-retina barrier because there is no diffusion barrier for blood-borne compounds available between the pecten and the retina. Surprisingly, the blood-retina barrier characteristics of this organ have not been studied so far, although the pecten oculi may constitute a fascinating model of vascular differentiation and barrier maturation: Pectinate endothelial cells grow by angiogenesis from the ophthalmotemporal artery into the pecten primordium and consecutively gain barrier properties. The pectinate pigmented cells arise during development from retinal pigment epithelial cells and subsequently lose barrier properties. These inverse transdifferentiation processes may be triggered by the peculiar microenvironment in the vitreous body. In addition, the question is discussed whether the avascularity of the avian retina may be due to the specific metabolic activity of the pecten.

Animals↗

PubMed1999

N-cadherin expression in endothelial cells during early angiogenesis in the eye and brain of the chicken: relation to blood-retina and blood-brain barrier development.

The factors responsible for the induction and maintenance of blood-brain barrier properties are still undefined. The process of blood-brain barrier formation is thought to take place in a two-stage manner: the initial commitment of vascular sprouts by neuroectodermal cells may be followed by the stabilization of barrier properties. In the present study, we investigated the expression pattern of neural (N)-cadherin during early angiogenesis in the brain and the pecten oculi of the chicken. The pecten has been introduced previously as a model for the investigation of the formation and maturation of barrier properties in the central nervous system. Whereas perineural and choroid vessels remained immunonegative for N-cadherin, vascular sprouts invading both the brain and the pecten primordium acquired anti-N-cadherin immunoreactivity. Confocal laser scanning and immunoelectron microscopy indicated that the antigen was located at the ablumenal endothelial membrane in contact with subendothelial cells. With the onset of barrier differentiation as determined by junctional restriction of the tight junction protein occludin, N-cadherin labelling rapidly decreased. Specific intraneuroectodermal upregulation and decline of endothelial N-cadherin was confirmed by in situ hybridization and suggests that N-cadherin expression by cerebral and pecteneal endothelial cells represents an initial and transient signal which may be involved in the commitment of early blood vessels to express blood-brain and blood-retina barrier properties.

Animals↗

PubMed1997

Maturation of the blood-retina barrier in the developing pecten oculi of the chicken.

The major interest in the development of the blood-brain barrier and its underlying induction mechanisms is given by the crucial role they play in the maturation of the central nervous system in general. Whilst it is believed that it is the microenvironment in the brain that destines the endothelial cells to become committed to barrier properties, the analysis of the multitude of factors probably responsible for this commitment is extremely difficult. Therefore, in a previous study, we inaugurated the pecten oculi of the avian eye as a relatively simple in vivo model of the blood-brain barrier [Gerhardt, S. et al, Cell Tissue Res., 285 (1996) 91-100]. In the present study, we demonstrate data on the development of the pecten which allow us to understand better the commitment of barrier properties in endothelial cells in an environment which is considerably less complex than that realized in the brain. The pecten is built up by mainly two cell types, the pigmented glial cells and the endothelial cells. The pigmented cells, which are believed to originate from the retinal pigment epithelium, lose their tight junctions in the microenvironment of the vitreous body, whereas the endothelial cells, which originate from the permeable choroidal vessels, gain tight junctions and other barrier properties in the microenvironment of the vitreous body. On embryonic day 7 (E7), tight and gap junctions between epithelial-like glial cells line the vitreal border of the developing pecten. By E16, these junctions disappear, and the endothelial cells gradually acquire barrier characteristics (continuous and P-face associated tight junctions, no extravasation of lanthanum nitrate, and the exclusive expression of the glucose transporter isoform 1 and the barrier specific antigen HT7 in their luminal and abluminal membranes). The results are discussed considering the switch from an epithelial (glial) to an endothelial barrier.

Animals↗

PubMed1996

The pecten oculi of the chicken as a new in vivo model of the blood-brain barrier.

The pecten oculi of White Leghorn chicken was investigated in terms of possible blood-brain barrier properties by means of light and electron microscopy. The morphology, histochemistry and immunocytochemistry of this intraocular blood vessel convolute was examined. The permeability of the blood vessel for the electron-dense tracer lanthanum-nitrate was also determined. The endothelia of the pectinal capillaries were found to be continuous, possessing elaborate tight junctions with a high P-face association in freeze-fracture images and a low incidence of vesicles. Two barrier-specific proteins, i.e. the HT7-antigen and the glucose transporter isoform GluT-1 were specifically and exclusively expressed by the endothelial cells. Endothelial cells also showed no paracellular or transcytotic extravasation of lanthanum-nitrate. We conclude that the endothelium of the pecten oculi is the site of the blood-retina barrier. Furthermore, we demonstrate that the unique morphological characteristics of the pecten make it advantageous as a new in vivo model for the investigation of the blood-brain barrier.

Animals↗

PubMed1990

[Ablation of the trabecular meshwork].

In an experimental investigation we examined the possibility to create an open pathway between the anterior chamber and Schlemm's canal by excimer laser ablation of the trabecualr meshwork (AT) in enucleated eyes. A quartzfiber was directed through the anterior chamber to the opposite chamber angle. With an energy of 0.3-1.5 mJ and wavelengths of 248 and 308 nm pores were easily made into the trabecular meshwork leading to a direct connection between the anterior chamber and Schlemm's canal. This result was confirmed by histologic examination of the globes. The trabecular meshwork has disappeared completely. The surrounding tissue reveals only minimal thermal effects due to the laser burns. With the same method cyclodialysis and basal iridectomy may be performed. The operation is simple and effects can be placed with great accuracy.

Animals↗

PubMed1990

[Gardner-Diamond syndrome].

This paper presents a 26-year-old woman with the characteristic features of Gardner-Diamond syndrome: recurrent painful bruises reproducible by intradermal injection of autologous red blood cells, and a "hysterical" personality pattern together with nonspecific multisystem complaints.

Adult↗

PubMed1986

[Ergotism with cerebral complications. Case report and review of the literature].

Abuse of ergotamine-containing suppositories was followed by generalized vessel stenoses in a pregnant 29-year-old migraine patient and led to a space-occupying great brain infarction in the area supplied by the right internal carotid artery. Impressive improvement of clinical, computed tomography and ultrasound findings was observed during treatment with nimodipine. The literature about cerebral symptoms of ergotism is reviewed.

Adult↗