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Biomedical subjects

W Schaper

Publications and source records attributed to W Schaper.

At least 55 records · Page 3Linked to original sources
PubMed1999

Arteriogenesis, the good and bad of it.

Arteriogenesis, the process of collateral artery growth as an adaptation to major arterial occlusion, can be life- and tissue saving and may alter the natural course of the consequences and organ manifestations of arterial disease. This is achieved by an active growth process that is coupled to complete arterial remodeling with activation of proteases and destruction of the organ tissue in the immediate vicinity of the growing vessel, to create the space for a new artery which expands to about 20 times its original diameter. Much of the growth and remodeling is achieved by attraction, adhesion, activation and invasion of circulating cells, mostly monocytes, but also T-cells and basophiles. Growth factors that are already present, as well as those that are produced by invading cells, produce an environment of inflammation and facilitate coagulation and are therefore pro-atherogenic. It will be a challenge for future therapies with growth factors, chemokines and cytokines to neutralize the atherogenic and to maximize their arteriogenic properties.

Animals↗
PubMed1999

Special communicationthe critical role of mechanical forces in blood vessel development, physiology and pathology

The following extended abstracts were presented at the Research Initiatives in Vascular Disease Conference, Movers and Shakers in the Vascular Tree-Hemodynamic and Biomechanical Factors in Blood Vessel Pathology, sponsored by The Lifeline Foundation and the Cardiovascular & Interventional Radiology Research and Educational Foundation; jointly sponsored by the International Society for Cardiovascular Surgery, North American Chapter, The Society for Vascular Surgery, and The Society of Cardiovascular and Interventional Radiology; in cooperation with the National Institutes of Health-National Heart, Lung &Blood Institute on Mar 11-12, 1999, in Bethesda, Md.

Journal Article↗
PubMed1999

VEGF and therapeutic opportunities in cardiovascular diseases.

In the past ten years, alternative revascularization strategies have come from bench to bedside focusing on the growth of new vessels to replace the old. Hypoxia and vascular endothelial growth factor may induce capillary growth; however, atherosclerosis affects large conductance vessels, which can only be replaced by functional collateral arteries.

Cardiovascular Diseases↗
PubMed1999

Okadaic acid and anisomycin are protective and stimulate the SAPK/JNK pathway.

We report that okadaic acid (OA), a known inhibitor of Ser/Thr phosphatases, protects pig myocardium against ischemic injury in an in vivo model and stimulates the activities of stress-activated protein kinases/c-Jun N-terminal kinases (SAPKs/JNKs). When OA was directly infused into the subsequently ischemic myocardium for 60 min before a 60-min period of coronary occlusion followed by reperfusion, infarct size was reduced from a control value of 83.4 +/- 2.8% of the risk region to 40.7 +/- 9.1%. When OA was infused for 10 min before a 5-min occlusion and during 45 min thereafter, infarct size was reduced to 26.5%. In a separate set of similar experiments, we pretreated pig hearts in vivo with the protein-synthesis inhibitor and known activator of SAPK/JNK, anisomycin (AN), and found that this compound also significantly reduced infarct size from 83.4 +/- 2.8.1% to 48.1 +/- 5.1%. For in vitro assays, OA (600 nM), AN (500 microM), or solvent (KHB) were locally infused into the left ventricular myocardium, and biopsies from in situ beating hearts were obtained after 10, 30, and 60 min of infusion. The activities of Ser/Thr phosphatases (PPases), especially PP-2A, were significantly decreased after OA infusion. OA infusion increased the activity (in-gel phosphorylation of N-terminal c-Jun1-135) of both 46- and 55-kDa SAPK/JNKs (twofold to threefold, 30 and 60 min of infusion), and this increase correlated well with the observed decrease of PPase activities. Western blot analysis with a phosphospecific SAPK/JNK (Thr 183/Tyr 185) antibody showed an increased content of the phosphorylated forms after OA treatment. We observed significant stimulation of SAPK/JNK activity also after AN treatment (threefold to fourfold, after 30 min of infusion). In contrast to the SAPK/JNKs, the infusion of both OA and AN did not significantly change the activities and phosphorylation of extracellular signal-related kinases (ERKs) and p38-MAPK. The findings that the protective effect of both OA and AN correlates with increased activity of SAPK/JNKs suggest the involvement of these enzymes in the mechanism of cardioprotection.

Animals↗
PubMed1999

Hypoxia induces permeability in brain microvessel endothelial cells via VEGF and NO.

In this study, an in vitro model of the blood-brain barrier, consisting of porcine brain-derived microvascular endothelial cells (BMEC), was used to evaluate the mechanism of hypoxia-induced hyperpermeability. We show that hypoxia-induced permeability in BMEC was completely abolished by a neutralizing antibody to vascular endothelial growth factor (VEGF). In contrast, under normoxic conditions, addition of VEGF up to 100 ng/ml did not alter monolayer barrier function. Treatment with either hypoxia or VEGF under normoxic conditions induced a twofold increase in VEGF binding sites and VEGF receptor 1 (Flt-1) mRNA expression in BMEC. Hypoxia-induced permeability also was prevented by the nitric oxide (NO) synthase inhibitor NG-monomethyl-L-arginine, suggesting that NO is involved in hypoxia-induced permeability changes, which was confirmed by measurements of the cGMP level. During normoxia, treatment with VEGF (5 ng/ml) increased permeability as well as cGMP content in the presence of several antioxidants. These results suggest that hypoxia-induced permeability in vitro is mediated by the VEGF/VEGF receptor system in an autocrine manner and is essentially dependent on reducing conditions stabilizing the second messenger NO as the mediator of changes in barrier function of BMEC.

Animals↗
PubMed1999

Cardiac microvascular endothelial cells express alpha-smooth muscle actin and show low NOS III activity.

We established a culture system of porcine coronary microvascular endothelial cells (MVEC) with high cellular yield and purity >98%. Endothelial origin was confirmed by immunostaining, immunoblotting and fluorescence-activated cell sorter (FACS) analysis using low-density lipoprotein uptake, CD31, von Willebrand factor, and the lectin Dolichos biflorus agglutinin. MVEC were positive for alpha-smooth muscle actin in culture and in myocardium, as confirmed by FACS. Of the primary MVEC, approximately 30% expressed nitric oxide synthase (NOS) III in numbers decreasing from the first passage (6 +/- 1%) to the second passage (4 +/- 1%; P < 0.001 vs. primary isolates), whereas approximately 100% of aortic endothelial cells (AEC) expressed NOS III. In AEC, NOS III activity (pmol citrulline. mg protein-1. min-1) was 80 +/- 10 and was nearly abolished in the absence of calcium (5 +/- 1, P < 0.001). In primary MVEC, however, NOS III activity in the presence and absence of calcium was 20 +/- 4 and 25 +/- 5, respectively. We conclude that cardiac MVEC, in contrast to AEC, contain alpha-smooth muscle actin, show low-grade NOS III activity, and provide a suitable in vitro system for the study of endothelial pathophysiology.

Actinin↗
PubMed1999

Microvascular endothelial cells remodel cultured adult cardiomyocytes and increase their survival.

We investigated the paracrine effect of cardiac microvascular endothelial cells (MVEC) on cultured adult rat cardiomyocytes (ARC). ARC were exposed for 8 days to serum-free medium (CM) conditioned by MVEC. Controls were grown in FCS or FCS-free medium. Protein synthesis of CM-stimulated ARC increased twofold versus 5% FCS-stimulated cells until day 8. Seventy-nine percent of CM-treated myocytes survived, whereas only twenty-four percent of FCS-free ARC retained viability. The phenotype of myocytes exposed to CM was different from control. Analysis by confocal laser microscopy of CM-stimulated myocytes showed actin staining throughout the whole cell body up to the peripheral extensions, with concomitant appearance of myomesin in a cross-striated pattern. The reexpression of fetal alpha-smooth muscle actin determined immunohistochemically and by Western blot increased from day 6 in CM-treated cells, whereas ARC grown in up to 20% serum were negative. These effects could not be mimicked by any of the other cardioactive substances tested here, indicating a novel trophic factor in CM.

Actins↗
PubMed1999

Ultrastructural assessment of myocardial necrosis occurring during ischemia and 3-h reperfusion in the dog.

To determine whether myocardial necrosis may occur during postischemic reperfusion, electron microscopy was used to identify morphological features of irreversible injury in myocardial samples taken from anesthetized dogs with 90-min ischemia and 0-, 5-, 90-, or 180-min reperfusion. In samples without detectable collateral blood flow, necrosis was almost complete, whether or not the myocardium was reperfused. In samples with collateral flow, necrosis was more frequent after 180-min reperfusion than in the absence of reperfusion, despite similar collateral flows in the two groups. Excess of necrosis after 180-min reperfusion was evident in endocardium (ischemia only: 4 of 13, 180-min reflow: 14 of 20; P = 0. 03) and midwall (ischemia only: 9 of 25, 180-min reflow: 29 of 45; P = 0.02). Multiple logistic regression with variables of collateral flow and transmural position was used to determine risk of irreversible injury in 111 samples from ischemic myocardium without reperfusion (model predictive accuracy = 75%, P < 0.00001) and to predict risk of necrosis in myocardium reperfused for 180 min. Of 65 samples from endocardium and midwall with detectable collateral flow, the model predicted necrosis in 23 samples but necrosis was observed in 43 samples (P < 0.01). Reperfusion duration was a determinant of frequency of irreversible injury. Multiple logistic regression for 186 samples from myocardium reperfused for 5, 90, or 180 min showed that reperfusion duration was an independent predictor of irreversible injury (P = 0.0003) when collateral flow and transmural location were accounted for. These findings are consistent with the occurrence of necrosis during reperfusion in myocardium exposed to substantial, prolonged ischemia but with sufficient residual perfusion to avoid necrosis during the period of flow impairment.

Animals↗
PubMed1998

Barbiturates decrease the expression of vascular endothelial growth factor in hypoxic cultures of porcine brain derived microvascular endothelial cells.

Vascular endothelial growth factor (VEGF) is known to be produced in higher amounts during hypoxia by a variety of cell types and has been shown to increase the permeability of brain derived microvascular endothelial cells (BMEC) during hypoxia by an autocrine mechanism. Because the barbiturates, methohexital (MH) and thiopental (TP), induced a dose-dependent reduction in hypoxia-induced permeability changes of BMEC, the effect of both barbiturates on the VEGF expression during hypoxia was investigated. Both barbiturates decreased the hypoxia-induced expression of VEGF in BMEC in a concentration-dependent manner. This effect is partly caused by the impairment of the hypoxia-induced VEGF mRNA stabilization. VEGF-induced permeability changes during normoxia were unaffected by the barbiturates suggesting that MH and TP are directly reducing hypoxia-induced VEGF synthesis. In conclusion, the inhibiting effect of these barbiturates on the hypoxia-induced VEGF expression results in the decreased permeability of the BMEC monolayer during hypoxia, which may contribute to the described neuroprotective action of barbiturates by reduction of brain edema formation.

Adenosine↗
PubMed1998

Monocyte activation in angiogenesis and collateral growth in the rabbit hindlimb.

We have previously shown that monocytes adhere to the vascular wall during collateral vessel growth (arteriogenesis) and capillary sprouting (angiogenesis). In this study we investigated the association of monocyte accumulation with both the production of the cytokines-basic fibroblast growth factor (bFGF) and TNF-alpha-and vessel proliferation in the rabbit after femoral artery occlusion. In particular, we studied the effects of an increase in monocyte recruitment by LPS on capillary density as well as collateral and peripheral conductance after 7 d of occlusion. Monocytes accumulated around day 3 in collateral arteries when maximal proliferation was observed, and stained strongly for bFGF and TNF-alpha. In the lower limb where angiogenesis was shown to be predominant, macrophage accumulation was also closely associated with maximal proliferation (around day 7). LPS treatment significantly increased capillary density (424+/-26.1 n/mm2 vs. 312+/-20.7 n/mm2; P < 0.05) and peripheral conductance (109+/-33.8 ml/min/100 mmHg vs. 45+/-6.8 ml/min/100 mmHg; P < 0.05) as compared with untreated animals after 7 d of occlusion. These results indicate that monocyte activation plays a major role in angiogenesis and collateral artery growth.

Animals↗
PubMed1998

Intramyocardial infusion of FGF-1 mimics ischemic preconditioning in pig myocardium.

Previous studies on the mRNA and protein level suggested a cardioprotective role of FGF-1. These presumed actions of FGF-1 and FGF-2, as well as the underlying mechanisms, were investigated in this study. Human recombinant FGF-1 (0.5 microgram/ml, 20 microliters/min) and FGF-2 (2 micrograms/ml) were applied by means of direct intramyocardial infusion (IM) for 60 min prior to a 60 min LAD-occlusion and 120 min reperfusion. Myocardial infarction compared to the region at risk was significantly decreased by FGF-1 and FGF-2 treatment (FGF-1: 51.8 +/- 7.7%, respectively. FGF-2: 57.3 +/- 6.5% v control 83.4 +/- 2.8%, P < 0.05). The increase in survival time was about 33 min, and equalled that of ischemic preconditioning. This effect was caused by the mitogenic part of the molecule, since infusion of a truncated version of FGF-1 (0.5-1 microgram/ml), lacking mitogenicity but maintaining hemodynamic activity, did not induce cardioprotection (78.3 +/- 0.73% v control 83.4 +/- 2.8%). Suramin (0.5 microgram/ml) prevented the observed cardioprotection (77.0 +/- 1.2% v control 83.4 +/- 2.8%) proving that the cardioprotective effect is receptor-mediated. Genistein (0.5 microgram/ml), an inhibitor of tyrosine kinases, abolished the cardioprotection as well (77.2 +/- 2.4% v control: 83.4 +/- 2.8%). Immunohistochemical staining revealed an uptake and translocation of exogenous FGF-1 to a (peri-)nuclear localization in myocytes and into non-myocytes for FGF-2. We conclude that both FGF-1 and FGF-2 are cardioprotective (FGF-1 being more active on a molar basis), and mimic ischemic preconditioning. Their actions are receptor-mediated and receptor activation is involved. Uptake and transport to a (peri-)nuclear localization, seems to be a pathway of minor relevance, since it could not be blocked by tyrosine kinase receptor inhibition. Tyrosine kinase-coupled receptor occupation in general is not protective as demonstrated by the lack of effect with VEGF-infusion.

Animals↗
PubMed1998

Vascular remodeling and altered protein expression during growth of coronary collateral arteries.

The cellular mechanism of growth of coronary collateral vessels (adaptive arteriogenesis) is still poorly understood. To define a possible role of an altered expression pattern of cellular and matrix proteins in this process we implanted a constricting device around the left circumflex artery in 25 canine hearts and sacrificed the animals at the time of initiation (3 weeks), high activity (6 weeks) and discontinuation (8 weeks) of vessel growth. Methods were electron microscopy, labeling with Ki-67, the TUNEL method and immunofluorescence with confocal laser microscopy. As described earlier, the collateral vessels increased in wall thickness by the formation of a neointima without luminal narrowing. We report here for the first time that extensive vascular remodeling including migration, proliferation and apoptosis in all cell types takes place during the growth phase but not in more mature vessels. The most obvious difference with normal vessels is the reiteration of an embryonal expression pattern in smooth muscle cells of the neointima which includes a significant reduction of desmin and alpha-smooth muscle actin, calponin and vinculin. Fibronectin as a promoter of migration and adhesion was abundant, its antagonist tenascin and chondroitin sulfate showed patchy localization. A completely new finding in arteriogenesis is the involvement of mast cells releasing histamine and serotonin and probably cytokines. Vascular protein expression returned to almost normal at 8 weeks indicating cessation of remodeling. We conclude that in collateral vessel development an altered cellular and matrix protein expression is involved in a drastic case of positive vascular remodeling finally resulting in mature vessels 20-fold increased in size which are capable of maintaining the functional and structural integrity of the myocardium at risk.

Actins↗
PubMed1998

Tumor necrosis factor-alpha is expressed by monocytes/macrophages following cardiac microembolization and is antagonized by cyclosporine.

The time course of expression of TNF-alpha in myocardial wound healing following ischemic injury was investigated in the porcine heart. Microembolization was used to induce focal ischemia and necrosis in hearts of 39 adult pigs. The animals were sacrificed after 3, 6, 12, 24 h, 3 and 7 days, and after 4 weeks, and the myocardial tissue was studied by immunofluorescence using specific antibodies. TNF-alpha containing cells were identified as monocytes/macrophages by double staining with a muramidase antibody. Monocytes/macrophages were the only source of TNF-alpha. Microembolization caused multiple necrotic foci with loss of myocytes in the left ventricular myocardium. These foci contained numerous monocytes/macrophages and showed an inflammatory reaction typical of wound healing followed by replacement with scar tissue. The number of TNF-alpha positive cells increased after 24 h, peaked between 3-7 days and slowly decreased thereafter. Expression of TNF-alpha in monocytes/macrophages was significantly reduced after pretreatment of pigs with cyclosporine or dexamethasone. It is concluded that 1.) in myocardial tissue monocytes/macrophages are the only cell type expressing TNF-alpha, 2.) TNF-alpha is involved in wound healing after ischemia, and 3.) synthesis of TNF-alpha and inflammatory angiogenesis can be inhibited be treatment with either cyclosporine or dexamethasone.

Animals↗
PubMed1998

Upregulated and downregulated transcription of myocardial genes after pulmonary artery banding in pigs.

BACKGROUND: Acute or chronic pressure overload may occur during or after cardiac surgical procedures. Typical examples are aortic cross-clamping and pulmonary artery banding. It is well known that mechanical stress induces transcription of different myocardial genes. However, these results were mainly obtained from in vitro studies and experiments with rodents. This experiment was carried out to investigate molecular alterations after pressure overload in porcine hearts. METHODS: The study was performed with 35 Landrace pigs with a mean weight of 32+/-1.2 kg. The five groups consisted of 7 pigs each, 3 sham-operated pigs and 4 banded pigs. The hearts were exised after different time intervals. We investigated messenger RNA expression of sarcoplasmic reticulum adenosine triphosphatase, phospholamban, alpha-/beta-myosin heavy chain, and atrial natriuretic factor by Northern blot analysis. RESULTS: The ratio of right ventricular weight to body weight increased significantly after 7 and 24 days in banded pigs (p < 0.05). Atrial natriuretic factor messenger RNA was significantly upregulated in banded pigs versus sham-operated pigs after 1 day (240%+/-7% versus 100%+/-6%; p < 0.01) and 3 days (520%+/-8% versus 100%+/-8%; p < 0.01). There was insignificant downregulation of sarcoplasmic reticulum adenosine triphosphatase and phospholamban after 1, 3, and 7 days. Myosin heavy chain messenger RNA expression remained unchanged. CONCLUSIONS: Pulmonary artery banding results in hypertrophic response of the porcine right ventricle; however, the weight increase is not the result of myosin heavy chain messenger RNA upregulation. Atrial natriuretic factor messenger RNA is locally expressed in mechanically stressed myocytes. Furthermore, pressure overload downregulates transcription of calcium-binding proteins that can influence ventricular contractility. These results may have an impact on cardiac surgical procedures.

Adenosine Triphosphate↗
PubMed1998

The delivery of angiogenic factors to the heart by microsphere therapy.

Microspheres offer the possibility of local noninvasive delivery of drugs over an extended period of time. We adsorbed fibroblast growth factor (FGF) to microspheres of precapillary size that were injected via a coronary catheter. We showed that FGF was released from these microspheres and taken up by endothelial cells, which proliferated following translocation of FGF to the nucleus. This method for application of growth factors allows the precise delivery of angiogenic substances to any selected part of the heart or other organs without causing inflammation or ischemia.

Animals↗