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R Bizios

Publications and source records attributed to R Bizios.

At least 55 records · Page 3Linked to original sources

RGDS tetrapeptide binds to osteoblasts and inhibits fibronectin-mediated adhesion.

The mechanisms of osteoblast attachment to surfaces were probed using the adhesive tetrapeptide RGDS (Arg-Gly-Asp-Ser) and the related but non-adhesive RGES (Arg-Gly-Glu-Ser). Specifically, RGDS and RGES were investigated for their ability both to bind to a suspension of well-characterized neonatal rat calvarial osteoblasts and to inhibit cell attachment to fibronectin-coated microtiter plates. RGDS bound to the cells with an average Kd approximately 9.4 x 10(-4) M, and RGES bound with an average Kd approximately 3.0 x 10(-4) M; at saturation, the osteoblasts bound almost twice as much RGDS as RGES. RGDS partially inhibited cell adhesion (55% to 60%) in a competitive, dose-dependent manner. In contrast, RGES had minimal effect on cell attachment. Since complete inhibition of attachment was not observed, it is likely that a synergistic adhesion site in the fibronectin molecule and/or cell surface molecules such as proteoglycans are active in mediating osteoblast/substrate adhesion.

Amino Acid Sequence↗

Thrombin-induced adherence of neutrophils to cultured endothelial monolayers: increased endothelial adhesiveness.

We examined the effects of alpha-thrombin on the adherence of neutrophils to endothelial cell monolayers. Endothelial cells derived from the ovine pulmonary artery and ovine neutrophils were used. Thrombin (10(-8) M) resulted in a time-dependent increase in neutrophil adherence to the endothelium. The response was concentration-dependent with a maximal response at 10(-8) M. Thrombin did not induce neutrophil adherence either to plastic or to endothelial cell-derived matrix. The adherence response was inhibited in the presence of alpha-thrombin that had been inactivated with anti-thrombin III (1U:1U) or with hirudin (1 U/ml). However, the addition of either anti-thrombin III or hirudin simultaneously with alpha-thrombin to the cultured endothelial monolayers did not prevent neutrophil adherence. The monoclonal antibody MoAb 60.3, which precipitates a complex of four neutrophil surface glycoproteins (CDw18) was used to further characterize the reaction. MoAb 60.3 decreased the thrombin-induced adherence of neutrophils to the endothelial monolayer. Addition of 10(-8) M thrombin to the endothelial monolayer for 60 min, followed by washing the endothelium with fresh medium, caused resting neutrophils to adhere to the endothelial monolayers. MoAb 60.3 decreased neutrophil adherence to the washed endothelium. The factor(s) responsible for adherence was partially transferable. Medium obtained from incubating endothelial monolayers with thrombin (10(-8) M) for 60 min, adding hirudin to the medium to inactivate thrombin, and transferring it to untreated endothelial monolayers, elicited neutrophil adherence. The response was less than that obtained with thrombin alone (22.9 +/- 2.3% vs. 12.9 +/- 3.3%). The results indicate that the catalytic site of the thrombin molecule is responsible for the adherent activity. Thrombin elicits a rapid activation of endothelial cells with a response that involves the expression of endothelial adhesion sites and sites that interact with the neutrophil CDw18 adhesive glycoprotein complex. In addition, soluble transferable factor(s) which are generated by the endothelium also contribute to thrombin-induced neutrophil adherence.

Animals↗

Thrombin enhances opsonized zymosan-induced chemiluminescence of neutrophils.

We examined the effects of alpha-thrombin (the native enzyme) on neutrophil activation as assessed by the measurement of chemiluminescence. alpha-Thrombin in physiological concentrations (10(-9)-10(-8)M) did not induce neutrophil chemiluminescence. However, when neutrophils were coincubated with opsonized zymosan and alpha-thrombin, the chemiluminescence response to opsonized zymosan was enhanced in a concentration-dependent manner. The neutrophil chemiluminescence responses to opsonized zymosan and to opsonized zymosan plus alpha-thrombin were dependent on the generation of oxygen-derived free radicals since the chemiluminescence was inhibited by superoxide dismutase. The results indicate that thrombin per se does not induce neutrophil chemiluminescence. However, thrombin enhances the chemiluminescence response to opsonized zymosan suggesting an interaction between thrombin and complement receptors in inducing neutrophil activation. The chemiluminescence response to thrombin and opsonized zymosan is the result of oxygen-derived free radicals.

Animals↗

Inhibition of human scleral fibroblast proliferation with heparin.

Proliferation of fibroblasts is a serious problem in ocular trauma and surgical wound healing. Depending on the location of the injury, the growth of fibroblasts can lead to different problems. In glaucoma filtering surgery, fibroblast proliferation may contribute to scar tissue formation and premature wound closure. Fibroblastic growth in proliferative vitreoretinopathy may lead to the formation of preretinal membranes, which can contract, causing retinal detachment. In an effort to find a more effective method of inhibiting ocular fibroblast proliferation, we have investigated the effect of heparin, a sulfated polysaccharide, on the proliferation of fibroblasts obtained from the sclera of donor eyes. Heparin inhibits the incorporation of 3H-thymidine in a dose-dependent manner in the presence of fetal bovine serum (FBS). This inhibition is partially reversed by endothelial cell growth factor (ECGF). The heparin antagonist protamine sulfate causes a reversal of heparin inhibition and, in some instances, a significant increase in 3H-thymidine incorporation compared to serum controls. Heparin was equally effective in inhibiting cell proliferation in control and heparin-protamine sulfate-pretreated medium. These results were apparently unrelated to a direct toxic effect on cells, as a Trypan Blue exclusion assay showed no significant difference in viability when heparin treated cells were compared to control cells. Direct cell counts showed that heparin was effective in inhibiting cell proliferation over a long time period, but only if it was reinstilled every 2 days. Heparin treatment shows promise as a method for controlling fibroblast proliferation in the eye.

Cell Division↗

Thrombin-induced thromboxane generation by neutrophils and lymphocytes: dependence on enzymic site.

We examined the effects of thrombin on thromboxane generation by sheep neutrophils and lymphocytes in vitro. Physiological concentration of thrombin (50 nM) resulted in thromboxane B2 generation from both neutrophils and lymphocytes, which was comparable to that obtained with zymosan activated serum challenge of the cells. Thromboxane B2 generation was dependent on the enzymic region of the thrombin molecule responsible for clotting activity because the complexing of thrombin with hirudin (1:1 U:U mixture of thrombin and hirudin) abolished thromboxane generation from both cell types. Further studies with modified forms of alpha-thrombin (which were produced by irreversible conjugation at the catalytic site and lacked enzymic activity) also showed no generation of thromboxane B2 from neutrophils or lymphocytes. The results indicate that thrombin stimulates thromboxane generation from neutrophils and lymphocytes and that this response is dependent on the proteolytic activity of thrombin.

Animals↗

Endothelial monolayer permeability to macromolecules.

The barrier function of the endothelial monolayer has not been extensively investigated using the cultured endothelium. The in vitro approach may contribute to a more complete understanding of microvessel wall permeability. Our studies using an in vitro endothelial monolayer system have led us to the following conclusions: the endothelial monolayer is more permeable to small-molecular-weight substances than to large molecules; the permeability of albumin is different for endothelial cells derived from different vascular sites (higher for pulmonary venous than pulmonary arterial endothelium); basement membrane components may have a significant role in the permeability of albumin across the endothelium; control of endothelial monolayer permeability is determined not only by the characteristics of the macromolecule (i.e., size and charge) but also by the shape of the endothelial cells and the size of interendothelial space.

Actins↗

Thrombin-induced increase in albumin permeability across the endothelium.

We studied the effect of thrombin on albumin permeability across the endothelial monolayer in vitro. Bovine pulmonary artery endothelial cells were grown on micropore membranes. Morphologic analysis confirmed the presence of a confluent monolayer with interendothelial junctions. Albumin permeability was measured by the clearance of 125I-albumin across the endothelial monolayer. The control 125I-albumin clearance was 0.273 +/- 0.02 microliter/min. The native enzyme, alpha-thrombin (10(-6) to 10(-10) M), added to the luminal side of the endothelium produced concentration-dependent increases in albumin clearance (maximum clearance of 0.586 +/- 0.08 microliter/min at 10(-6) M). Gamma (gamma) thrombin (10(-6) M and 10(-8) M), which lacks the fibrinogen recognition site, also produced a concentration-dependent increase in albumin clearance similar to that observed with alpha-thrombin. Moreover, the two proteolytically inactive forms of the native enzyme, i-Pr2 P-alpha-thrombin and D-Phe-Pro-Arg-CH2-alpha-thrombin, increased the 125I-albumin clearance (0.610 +/- 0.09 microliter/min and 0.609 +/- 0.02 microliter/min for i-Pr2 P-alpha-thrombin and D-Phe-Pro-Arg-CH2-alpha-thrombin at 10(-6) M, respectively). Since the modified forms of thrombin lack the fibrinogen recognition and active serine protease sites, the results indicate that neither site is required for increased albumin permeability. The increase in albumin clearance with alpha-thrombin was not secondary to endothelial cell lysis because lactate dehydrogenase concentration in the medium following thrombin was not significantly different from baseline values. There was also no morphological evidence of cell lysis. Moreover, the increase in 125I-albumin clearance induced by alpha-thrombin was reversible by washing thrombin from the endothelium. The basis for the increased albumin permeability following the addition of alpha-thrombin appears to be a reversible change in endothelial cell shape with formation of intercellular gaps.

Animals↗

Thrombin-induced chemotaxis and aggregation of neutrophils.

Thrombin-induced neutrophil chemotaxis and aggregation were studied using cells isolated from either human or sheep blood. Sheep neutrophils (10(8) cells/ml) exhibited maximum chemotactic migration towards 10(-8)M human alpha-thrombin, 10(-8)M gamma-thrombin (which lacks the fibrinogen site), and 10(-12)MD-Phe-Pro-Arg-CH2-alpha-thrombin (catalytically inactive thrombin). Chemotactic responses of the same magnitude were obtained with human neutrophils (10(8) cells/ml). The chemotactic responses to thrombin were comparable to those obtained with diluted (1:200 v/v) zymosan activated serum (ZAS) and 10(-11)M FMLP. Premixing of the thrombin forms with hirudin in 1:1 stoichiometric amounts abolished the chemotaxis but not chemokinesis Aggregatory responses of human and sheep neutrophils were comparable for ZAS, alpha-thrombin, and gamma-thrombin. The responses of both human and sheep neutrophils to D-Phe-Pro-Arg-CH2-alpha-thrombin were attenuated, indicating that the proteolytic site may be involved in the aggregatory response. The results suggest that thrombin-induced neutrophil chemotaxis and aggregation are mediated by different mechanisms, since chemotaxis is a catalytically independent response whereas aggregation is an active site independent response.

Animals↗

Pulmonary hemodynamic effects of antisheep serum-induced leukopenia.

Antisheep antileukocyte serum (ALS) was produced in rabbits, purified, and adsorbed against erythrocytes and platelets. The ALS was infused intra-arterially over a 3-hour period into anesthetized sheep (n = 6) prepared with lung lymph fistulas. Pulmonary vascular resistance (PVR) and pulmonary lymph flow (Qlym) increased two- to threefold while the lymph-to-plasma protein concentration ratio (L/P) did not change from baseline, suggesting an increase in pulmonary vascular permeability to proteins. The arterial leukocyte count decreased from 4,935 +/- 840 to 1,385 +/- 325 cells/microliters, the neutrophil count decreased from 1,045 +/- 265 to 340 +/- 130 cells/microliters, and the platelet count decreased from 2.8 X 10(5) +/- 0.2 X 10(5) to 0.65 X 10(5) +/- 0.12 X 10(5) cells/microliters. ALS induced neutrophil aggregation in vitro, but not platelet aggregation. In the present study, we also examined the effects of ALS-induced leukopenia on the increase in pulmonary vascular permeability after intravenous alpha-thrombin challenge to assess the role of leukocytes in mediating the increased permeability response. Sheep (n = 5) were made leukopenic by an intramuscular injection of ALS; Qlym was in the normal range 4 to 5 hours after the ALS administration. In the leukopenic group, thrombin challenge caused an increase in Qlym from 7.8 +/- 0.7 to 12.9 +/- 1.9 ml/hr (a 64% increase) while L/P decreased from 0.86 +/- 0.04 to 0.70 +/- 0.05 (a 19% decrease). In contrast, thrombin-induced intravascular coagulation in control sheep (n = 5) produced a 250% increase in Qlym with an increase in L/P. The results indicate that leukocytes are required for the increase in lung vascular permeability after thrombin-induced intravascular coagulation.

Animals↗

Thrombin-induced alterations in endothelial permeability.

Figure 15 summarizes the current understanding of mechanisms of endothelial permeability alterations induced with thrombin. If thrombin generation exceeds the antiprotease activity, thrombin results in clotting of fibrinogen and intravascular fibrin accumulation. Pulmonary neutrophil sequestration also occurs after fibrin deposition, and this is related to the degree and duration of fibrin sequestration. Neutrophil activation appears to be an essential requirement for the mediation of the pulmonary vascular injury. Thrombin-induced intravascular coagulation results in the generation of lipid mediators (LTB4 and HETEs), which may be involved in increasing endothelial permeability. The release of thrombin in higher concentrations during lysis of fibrin (sequence; see text) FIGURE 15. Hypothesis showing mechanisms of thrombin-induced increase in endothelial permeability to proteins. Thrombin may have direct effects on endothelial permeability, or thrombin induced fibrinogen clotting, activation of neutrophils, and the release of lipid metabolites that subsequently lead to an increase in endothelial permeability. clots may induce a direct formation of interendothelial "gaps." Therefore, the vascular injury induced by neutrophil activation and the formation of endothelial "gaps" induced directly by thrombin can both increase the endothelial permeability to proteins. Thrombin is an important mediator of increased endothelial permeability to macromolecules, and may participate in the inflammatory response. In this regard, thrombin may be similar to other mediators (such as histamine and serotonin) that have been previously documented to increase macromolecule transport across the endothelium. The implications of free thrombin in increasing endothelial permeability may be greater because thrombin not only has a direct effect on endothelial permeability, but also induces clotting of fibrinogen and the subsequent generation of mediators that activate neutrophils and that in turn can induce endothelial injury.

Actin Cytoskeleton↗

Pulmonary vascular response to platelet-activating factor in awake sheep and the role of cyclooxygenase metabolites.

We examined the effects of platelet activating factor (PAF) (1.0 microgram/kg infusion for 15 min) on pulmonary hemodynamics and lung fluid balance and the role of cyclooxygenase metabolites in mediating these responses in unanesthetized sheep prepared with lung lymph fistulas. Platelet activating factor infusion resulted in immediate and transient increases in pulmonary artery pressure, pulmonary vascular resistance, and pulmonary lymph flow. The lymph-to-plasma protein concentration ratio did not change significantly from baseline. Circulating platelet and leukocyte counts decreased immediately after PAF infusion; the leukopenia was the result of a rapid decrease in both the neutrophil and mononuclear leukocyte counts. Arterial thromboxane B2 (TxB2) concentration increased after the PAF infusion, but the 6-keto prostaglandin F1 alpha (a prostacyclin degradation product) concentration did not change from baseline. A chemically similar substance, Lyso-PAF, had no effect on the pulmonary hemodynamic, lymph, and hematologic parameters or the TxB2 generation. Administration of cyclooxygenase inhibitors, meclofenamate or indomethacin, prior to PAF infusion prevented thromboxane B2 generation and attenuated the pulmonary hemodynamic response. The initial pulmonary lymph flow and transvascular protein clearance (lymph flow times lymph-to-plasma protein concentration) responses to PAF were attenuated after cyclooxygenase inhibition. However, there were time-dependent increases in pulmonary lymph flow and transvascular protein clearance in the cyclooxygenase-inhibited groups. These results indicate that PAF induces pulmonary vasoconstriction mediated by cyclooxygenase metabolites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Effects of high frequency ventilation on lung lymph dynamics and prostaglandin generation.

We examined the consequences of high frequency ventilation (HFV) on pulmonary lymph flow (Qlym) in normal lungs and after the lymph flow was increased with an i.v. histamine infusion (2 micrograms/kg/min). Studies were made in the anesthetized sheep prepared with lung lymph fistulas. The sheep were subjected to intermittent positive pressure ventilation (IPPV) (frequency (f) = 12 breaths/min, tidal volume (TV) = 10 ml/kg) and HFV (f = 7 Hz, TV = 1-2 ml/kg). TV was adjusted prior to the experiment to achieve normal arterial blood gases. Histamine infusion doubled Qlym and lymph protein clearance (Qlym X lymph-to-plasma protein concentration ratio) from baseline. HFV did not affect Qlym and lymph protein clearance in normal lungs or after histamine infusion. HFV also did not result in generation of thromboxane (TxA2) and prostacyclin because plasma concentrations of their stable degradation products, TxB2 and 6-ketoprostaglandin F1 alpha, were not significantly elevated. The results indicate that HFV does not alter lymphatic pumping in the normal lung and during increased transcapillary protein transport.

Animals↗

Pulmonary neutrophil kinetics in sheep: effects of altered hemodynamics.

We investigated the effect of elevated left atrial pressure and reduced cardiac output on pulmonary neutrophil kinetics in the sheep. Sheep neutrophils were isolated, labeled with 111In-oxine, and reinfused. Erythrocytes were labeled with [99mTc]pertechnetate. A gamma camera measured the lung activities of the labeled neutrophils and erythrocytes. The results indicated that 38.5% of the total injected neutrophils marginated in the lung. Pulmonary hemodynamics were altered by inflating a left atrial balloon three times in each sheep for 15-30 min to achieve 5- to 25-mmHg increments in pulmonary arterial wedge pressure. At least a 30-min recovery period was allowed between inflations. After each left atrial balloon inflation, neutrophil uptake remained unchanged from base line, despite decreased mean cardiac output to 0.67 +/- 0.24 (+/- SD) 1/min and increased pulmonary blood volume. The absence of pulmonary neutrophil uptake was confirmed by arterial-venous measurements. Increased pulmonary blood volume had little effect on lung neutrophil uptake, suggesting that most of the pulmonary neutrophils are marginated. We conclude that the lungs have a large marginated neutrophil pool compared with the circulating pool and that reduced cardiac output and elevated left atrial pressure have no effect on pulmonary neutrophil kinetics in the sheep.

Animals↗

Pulmonary microvascular effects of arachidonic acid metabolites and their role in lung vascular injury.

Arachidonic acid metabolites produced by cyclooxygenase and lipoxygenase pathways affect pulmonary transvascular fluid and protein fluxes after pulmonary microvascular injury. Some of these products may contribute to the increase microvascular endothelial permeability whereas others may increase pulmonary microvascular filtration pressure. Prostaglandin (PG) E2, PGF2 alpha and cyclic endoperoxides increase microvascular pressure and thus increase the transvascular fluid filtration rate. Thromboxanes increase microvascular pressure and in addition may promote neutrophil adherence to endothelium and platelet aggregation, whereas prostacyclin has opposing actions. The cysteine-containing leukotrienes (LTs) (LTC4, LTD4, and LTE4) increase pulmonary microvascular pressure via a thromboxane-mediated mechanism, and LTB4 may increase pulmonary vascular permeability. Arachidonic acid metabolites do not appear to alter directly pulmonary endothelial membrane permeability but may contribute to the increased permeability by their actions on blood-formed elements. The pulmonary vasoconstrictor arachidonic aid metabolites increase microvascular hydrostatic pressure and may thereby enhance the degree of pulmonary edema.

Animals↗

Pulmonary neutrophil kinetics after thrombin-induced intravascular coagulation.

Previous studies have indicated that neutrophils are required for the development of increased lung vascular permeability after thrombin-induced pulmonary microembolization. In this study, we examined neutrophil kinetics and uptake in the sheep lung before and after lung vascular injury. Sheep neutrophils were isolated by a Percoll-gradient method and labeled with indium-111 oxine. A maximum lung activity of 40% of the injected indium-111 neutrophil activity was attained 8-12 min after the injection. The calculated half-lives of both circulating and pulmonary neutrophils were 700 min. The rate of washout of labeled neutrophils from the lungs was the same as the loss of the peripheral blood activity, indicating removal of neutrophils from the lung and blood by a common pathway (e.g., liver and spleen). Intravenous infusion of alpha-thrombin resulted in an immediate uptake of neutrophils of 14% above the base-line activity. The increased uptake was associated with an immediate decrease in the blood activity, indicating sequestration of the neutrophils in the pulmonary circulation. The neutrophil uptake after alpha-thrombin was transient, reaching a maximum 15 min after infusion. Neutrophil uptake did not occur with alpha-thrombin (which lacks the fibrinogen recognition site), suggesting that the uptake was secondary to intravascular coagulation. An increase in the pulmonary blood volume cannot explain the increased neutrophil sequestration because pulmonary blood volume determined by [99mTc]pertechnetate-labeled erythrocytes did not increase after the alpha-thrombin infusion. Therefore, alpha-thrombin results in a transient neutrophil sequestration in the lung, and the response is secondary to the intravascular coagulation induced by the alpha-thrombin.

Animals↗

Comparison of alpha- and gamma-thrombin on lung fluid balance in anesthetized sheep.

We examined the effects of varying dosages of thrombin on lung fluid balance in halothane-anesthetized sheep prepared with lung lymph fistulas. A 15-min iv infusion of sublethal doses of alpha-thrombin (2.5 clotting units/micrograms), the native enzyme, at 0.6 or 1.1 nmol active enzyme/kg body wt increased the mean pulmonary arterial pressure (Ppa) and pulmonary vascular resistance (PVR) two- to threefold. Neither parameter increased in a dose-dependent manner. Platelet counts decreased 50% with both dosages. Leukocyte counts decreased 35 and 75% from base line in the low- and high-dosage groups, respectively, and reached comparable levels of 50% below base line at 60-min postinfusion in both groups. Plasma fibrinogen concentrations decreased in a dose-dependent manner preceding dose-dependent increases in pulmonary lymph flow (Qlym) and lymph protein clearance (Clym). Fibrin deposition in pulmonary vessels was greater at 30 than at 180 min postinfusion. In contrast, a 15-min iv infusion of gamma-thrombin (0.002 clotting units/micrograms), which lacks the fibrinogen recognition site, at 1.2 nmol active enzyme/kg produced no significant increases in PVR, Ppa, Qlym, or Clym. The fibrinogen concentration did not change significantly, whereas platelet and leukocyte counts decreased 25% within 15 min. Fibrin microthrombi were less prominent in pulmonary vessels. Fibrin deposition associated with intravascular coagulation may be an important factor mediating thrombin-induced increases in pulmonary transvascular fluid and protein exchange.

6-Ketoprostaglandin F1 alpha↗

Effects of cyclooxygenase and lipoxygenase inhibition on lung fluid balance after thrombin.

We examined the roles of the cyclooxygenase and lipoxygenase pathways in the alterations in lung fluid and protein exchange after pulmonary microembolism. Infusion of alpha-thrombin (T) (55 +/- 13 U/kg) immediately increased mean pulmonary arterial pressure (Ppa) and mean pulmonary vascular resistance (PVR), but both Ppa and PVR waned with time after T. Cyclooxygenase inhibition with either indomethacin or ketoprofen produced sustained increases in Ppa and PVR. The initial increases in Ppa in the cyclooxygenase-inhibited groups (CI) were matched to the control group by administering greater amounts of T. In the control group, T rapidly increased pulmonary lymph flow (Qlym) by two- to threefold, and this was associated with a steady increase in lymph-to-plasma protein concentration ratio (L/P). In contrast, in cyclooxygenase-inhibited (CI) groups, Qlym increased gradually to greater levels than in the control group, and L/P did not change. The effect on lung vascular permeability was determined by inflating a left atrial balloon catheter to raise pulmonary capillary pressure (Pc). An increase in Pc after T in the control group further increased Qlym and did not change L/P, whereas the increase in Pc after T in CI groups further increased Qlym and decreased L/P, indicating that cyclooxygenase inhibition prevented the increase in permeability. We determined whether lipoxygenase activation contributed to the increase in Qlym in CI groups by examining the effects of BW755C, an inhibitor of both cyclooxygenase and lipoxygenase pathways. BW755C resulted in the same increase in Qlym after T as in the control group, but the increase in Qlym was associated with a decrease in L/P. Therefore, inhibition of both pathways prevented the permeability increase and the greater increase in Qlym. The results indicate that cyclooxygenase and lipoxygenase pathways contribute to the increases in pulmonary transvascular fluid and protein fluxes after thrombin.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗