Modulation of cultured pulmonary microvessel and arterial endothelial cell barrier structure and function by serotonin

Syk Inhibition Induces Platelet Dependent Peri-islet Hemorrhage in the Rat Pancreas

Spleen tyrosine kinase (Syk) is a nonreceptor tyrosine kinase that is an important signaling enzyme downstream of immunoreceptors containing an intracellular immunoreceptor tyrosine activating motif (ITAM). These receptors encompass a wide variety of biological functions involved in autoimmune disease pathogenesis. There has been considerable interest in the development of inhibitors of the Syk pathway for the treatment of rheumatoid arthritis and systemic lupus erythematosus. We report that Syk inhibition mechanistically caused peri-islet hemorrhages and fibrin deposition in the rat pancreas and that this finding is due to a homeostatic functional defect in platelets. In more limited studies, similar lesions could not be induced in mice, dogs, and cynomolgus monkeys at similar or higher plasma drug concentrations. Irradiation-induced thrombocytopenia caused a phenotypically similar peri-islet pancreas lesion and the formation of this lesion could be prevented by platelet transfusion. In addition, Syk inhibitor-induced lesions were prevented by the coadministration of prednisone. A relatively greater sensitivity of rat platelets to Syk inhibition was supported by functional analyses demonstrating rat-specific differences in response to convulxin, a glycoprotein VI agonist that signals through Syk. These data demonstrate that the Syk pathway is critical in platelet-endothelial cell homeostasis in the peri-islet pancreatic microvasculature in rats.

Molecular Biology of Chronic Thromboembolic Pulmonary Hypertension

Recent efforts have seen major advances in elucidating the mechanisms underlying pulmonary arterial hypertension. However, chronic thromboembolic pulmonary hypertension (CTEPH) often has been excluded from these studies. Consequently, whereas the clinical, radiographic, and hemodynamic characteristics of CTEPH have been well described, there remains a deficit in our understanding of the cellular, molecular, and genetic mechanisms underlying CTEPH. Furthermore, although prior venous thromboembolism may act as the inciting event, it is still unclear what predisposes some patients to develop CTEPH. CTEPH has two major pathogenic components. The first is the primary obstruction of central pulmonary arteries by accumulation of thrombotic material. The second is characterized by severe pulmonary vascular remodeling, similar to that seen in idiopathic pulmonary arterial hypertension. Other articles in this series describe the pathological, surgical, and therapeutic aspects of CTEPH. Here, we review the potential molecular and cellular mechanisms that may contribute to the pathogenesis of CTEPH.

Histamine reduces gap junctional communication of human tonsil high endothelial cells in culture

The regulation of gap junctional communication by histamine was studied in primary cultures of human tonsil high endothelial cells (HUTECs). We evaluated intercellular communication, levels, state of phosphorylation, and cellular distribution of gap junction protein subunits, mainly connexin (Cx)43. Histamine induced a time-dependent reduction in dye coupling (Lucifer yellow) associated with reduction in connexin43 localized at cell-cell appositions (immunofluorescence), without changes in levels and phosphorylation state of connexin43 (immunoblots). These effects were prevented with chlorpheniramine, an H1 receptor blocker; indomethacin, a cyclooxygenase blocker; or GF109203X, a protein kinase C inhibitor. Treatment with phorbol myristate acetate, a protein kinase C activator, and 4bromo (4Br)-A23187, a calcium ionophore, mimicked the histamine-induced effects on dye coupling. 8Bromo-cAMP doubled the dye coupling extent and prevented the histamine-induced reduction in incidence of dye coupling. After 24-h histamine treatment, known to desensitize H1 receptors, reapplication of histamine increased cell coupling in a way prevented by ranitidine, an H2 receptor blocker. Thus, activation of H1 and H2 receptors, which increase intracellular levels of free Ca2+ and cAMP, respectively, may affect gap junctional communication in opposite ways. Stabilization of actin filaments with phalloidine diminished but did not totally prevent histamine-induced cell shape changes and reduction in dye coupling. Hence, the histamine-induced reduction in gap junctional communication between HUTEC is mediated by cytoskeleton-dependent and -independent mechanisms and might contribute to modulate endothelial function in lymphoid tissue.

Bradykinin and histamine generation with generalized enhancement of microvascular permeability in neonates, infants, and children undergoing cardiopulmonary bypass surgery

OBJECTIVE

To investigate whether generation and liberation of bradykinin and histamine contribute to generalized edema formation in pediatric cardiopulmonary bypass surgery.

DESIGN

Prospective observational study.

SETTING

Pediatric heart surgery of a university hospital.

PATIENTS

Forty-one neonates, infants, and children undergoing cardiopulmonary bypass to correct congenital cardiac anomalies.

INTERVENTIONS

Plasma concentrations of bradykinin and histamine were determined before, during, and after cardiopulmonary bypass. Fluid balance was evaluated by control of fluid intake and output.

MEASUREMENTS AND MAIN RESULTS

The susceptibility to generalized edema formation increased significantly (r = -.457; p <.005) with decreasing age. Approximately three times higher plasma concentrations of bradykinin (p <.001) were found at the onset of anesthesia and during the total observation period in patients with a fluid retention of >6% of body weight compared with patients with a lower retention rate. Plasma bradykinin reached significantly (p <.01) higher peak concentrations of 237.9 +/- 58.6 fmol/mL during cardiopulmonary bypass and of 227.5 +/- 90.7 fmol/mL during the early postoperative period in patients with severe edema formation in contrast to only 86.6 +/- 10.9 and 65.5 +/- 26.8 fmol/mL in patients with minor fluid retention. A tendency (p =.06) to slightly increasing histamine concentrations from 2.07 +/- 0.13 nmol/L at baseline to 3.32 +/- 1.41 nmol/L during 90 mins of cardiopulmonary bypass was only observed in patients with high fluid retention.

CONCLUSIONS

Bradykinin seems to be essentially involved in the enhancement of microvascular permeability in pediatric cardiopulmonary bypass surgery, although a dominant causal role cannot be claimed by this study. Histamine, however, doesn't appear to play a major role and may only contribute as a cofactor. To what extent an increased expression of bradykinin-1 and bradykinin-2 receptors or a reduced potential of bradykinin-degrading enzymes is involved is the object of a further clinical study.

Adenosine prevents permeability increase in oxidant-injured endothelial monolayers

Adenosine is thought to prevent or reduce the increase in permeability, which is a hallmark of oxidant injury to endothelium. However, the effect of adenosine on endothelial cells directly exposed to oxidant species has not been demonstrated in vitro. By measuring the passage of Evan's blue dye-labeled albumin across confluent monolayers, we demonstrated the ability of adenosine (0.1-100 microM) to lower basal permeability of human umbilical vein endothelial cells in a concentration-dependent fashion and prevent the permeability increase induced by exposure of the cells to xanthine plus xanthine oxidase (X/XO). Whereas pretreatment of monolayers for 10 min with adenosine (10 and 100 microM) prevented the X/XO-induced permeability increase, these same concentrations of adenosine failed to increase intracellular adenosine 3',5'-cyclic monophosphate in X/XO-exposed cells. The protective effect of adenosine on endothelial monolayers was mimicked by adenosine amine congener and 5'-(N-ethylcarboxamido)adenosine but not by other agonists examined. Hence, the protective effect of adenosine against oxidant injury may include an adenosine 3',5'-cyclic monophosphate-independent mechanism by direct action of adenosine at A1 receptors on endothelial cells.

Activation of endothelial cell kinin receptors leads to intracellular calcium increases and filamin translocation: regulation by protein kinase C

Membrane-associated cytoskeletal proteins provide support for endothelial cell (EC) junctional cell adhesion molecules. Nonmuscle filamin is a dimeric actin cross-linking protein that interacts with F-actin and membrane glycoproteins. Both bradykinin and des-Arg9-bradykinin cause filamin redistribution from the plasma membrane to the cytosol of confluent EC. Kinin-induced filamin translocation parallels the dynamics of intracellular Ca2+ increases. Pretreatment with kinin receptor antagonists blocks the Ca2+ response as well as filamin translocation induced by kinins. Protein kinase C activation prior to kinin stimulation attenuates intracellular Ca2+ increases and filamin translocation. BAPTA, a cell-permeable Ca2+ chelator, attenuates bradykinin-induced intracellular Ca2+ increases and filamin translocation. This study demonstrates that bovine pulmonary artery ECs express both kinin B1 and B2 receptors, and that activation of either receptor leads to intracellular Ca2+ increases. This Ca2+ signalling, which is downregulated by protein kinase C activation, is essential for kinin-induced filamin translocation.

Activation of thromboxane receptors and the induction of vasomotion in the hamster cheek pouch microcirculation

1. The present study was designed to investigate a possible role of thromboxane A2 (TXA2) on arteriolar vasomotion (spontaneous rhythmic variations of the vessel diameter). Therefore the microcirculatory effects of the thromboxane-receptor (TP-receptor) agonist, U 46619, as well as the effects of the TP-receptor antagonists S 17733 and Bay U3405 were evaluated in the hamster cheek pouch microcirculation. For comparison some effects of angiotensin II were also investigated. 2. For microcirculatory measurements, the cheek pouch preparation was placed under an intravital microscope coupled to a closed circuit TV system. The TV monitor display was used to obtain arteriolar internal diameter measurements by means of an image shearing device. 3. Superfusion (0.1 nM to 1 microM) or bolus application (1 pmol to 10 nmol) of U 46619 concentration- or dose-dependently decreased the arteriolar diameter and induced vasomotion in arterioles with a mean initial diameter of 24+/-2 microm. Both the vasoconstriction and the vasomotion induced by U 46619 were inhibited by the TP-receptor antagonists S 17733 (100 mg kg(-1), i.v.) and Bay U3405 (10 mg kg(-1), i.v.). 4. Bolus applications of angiotensin II (0.1 pmol to 1 nmol) induced transient vasoconstriction followed by vasodilatation in the cheek pouch arterioles. The dilatation but not the constriction, was sensitive to treatment with the NO-synthase inhibitor N(omega)-nitro-L-arginine (L-NOARG; 100 microM). Angiotensin II did not induce vasomotion in control conditions or in the presence of L-NOARG. 5. Bolus application of phenylephrine (10 pmol) induced vasoconstriction but no vasomotion in previously quiescent hamster cheek pouch arterioles. 6. These results indicate that activation of TP-receptors causes vasomotion in the hamster cheek pouch arterioles. These spontaneous rhythmic variations in arteriolar diameter are not observed with equipotent doses of angiotensin II and phenylephrine. Thus, the vasoconstriction by itself cannot explain the occurrence of vasomotion observed with the TP-receptor agonist.

A novel anti-inflammatory peptide inhibits endothelial cell cytoskeletal rearrangement, nitric oxide synthase translocation, and paracellular permeability increases

The endothelial cell (EC) membrane-cytoskeletal interface in part maintains plasma membrane integrity and promotes cell-cell apposition. Nonmuscle filamin (ABP-280), an actin crosslinking protein, promotes orthogonal branching of F-actin and is the major protein that links the peripheral actin network to the plasma membrane through its C-terminal glycoprotein binding site. In response to bradykinin, filamin translocates from the cell periphery to the cytosol within 1 min. A synthetic peptide, corresponding to filamin's C-terminal calcium/calmodulin-dependent protein kinase II phosphorylation site (CaM peptide), prevents calcium-activated filamin translocation in permeabilized bovine pulmonary artery EC. The myristoylated permeable form of this peptide inhibits bradykinin-induced filamin translocation and F-actin rearrangement in cultured intact ECs. In addition, bradykinin-induced paracellular gap formation is significantly attenuated by CaM peptide, which suggests that the presence of a filamin-based peripheral F-actin network is essential for maintaining EC barrier function. Moreover, CaM peptide reduces wound-induced EC migration rate by 40%, which indicates that F-actin rearrangement is required for efficient cell motility. The CaM peptide affects other bradykinin-induced inflammatory responses. EC nitric oxide synthase (eNOS) translocates from the cell membrane to the nuclear fraction within 1-2 min of bradykinin treatment. Pretreatment with CaM peptide inhibits eNOS translocation. However, the peptide has no effect on bradykinin-induced von Willebrand Factor release. In summary, the CaM peptide exhibits several anti-inflammatory properties that include maintaining EC junctional stability and inhibiting eNOS translocation.

Comparative cytotoxicity of monocrotaline and its metabolites in cultured pulmonary artery endothelial cells

Metabolites of the pyrrolizidine alkaloid monocrotaline cause progressive development of pulmonary hypertension in rats. The putative reactive intermediate monocrotaline pyrrole (MCTP) has been shown to cause cytotoxicity, hypertrophy, decreased proliferation, and altered synthetic capability in cultured pulmonary endothelial cells. We compared effects of monocrotaline (MCT) at 60 micrograms/ml (0.185 mM) with previously identified metabolites, MCTP 10 micrograms/ml (0.031 mM) and glutathione-conjugated dihydropyrrolizine (GSH-DHP) 60 micrograms/ml (0.135 mM), in cultured bovine pulmonary artery endothelial cells (BPAECs). To determine whether endothelial metabolism might contribute to the mechanism of this toxicity, we used markers of cytotoxicity (LDH release), synthetic activity (PGI2 synthesis), hypertrophy (planimetry), cell density (cell count/area), and Evans blue albumin (EBA) transudation as a marker for loss of fluid barrier integrity. We found changes in all endothelial markers with MCTP only. MCTP caused increased LDH release by 48 hr, augmented PGI2 synthesis by 96 hr, and resulted in hypertrophy and decreased cell density by 48 hr that persisted at least 21 days. There was increased EBA transudation at 24 hr posttreatment. We concluded that, based on markers of endothelial damage, BPAECs showed no apparent ability to metabolize MCT to a reactive intermediate nor to further metabolize GSH-DHP to a toxic species. We also concluded that MCTP can cause a direct effect on fluid barrier integrity of endothelial cell monolayers in the absence of inflammation.

A luminescent europium complex for the sensitive detection of proteins and nucleic acids immobilized on membrane supports

Certain metal complexes selectively interact with proteins immobilized on solid-phase membrane supports to form brightly colored products. Detecting the absorbance of colorimetric stains is limited by the molar extinction coefficient of the product, however. Development of light-emitting complexes should improve detection sensitivity, but fluorescent labels described to date modify free amino, carboxyl, or sulfhydryl groups often rendering proteins unsuitable for further analysis. Bathophenanthroline disulfonate (BPSA) forms a luminescent europium (Eu) complex that reversibly binds to proteins and nucleic acids. Analysis of charge-fractionated carrier ampholytes and synthetic polymers of different L-amino acids indicates that protein binding is chiefly through protonated alpha- and epsilon-amino side chains. Proteins or nucleic acids immobilized to a nitrocellulose or polyvinyl difluoride membrane by electroblotting, dot-blotting, or vacuum slot-blotting are incubated with the lanthanide complex at acidic pH. Membranes are rinsed, illuminated with UV light and the phosphorescence of BPSA-Eu is measured at 590 to 615 nm using a CCD camera or spectrofluorimeter. The linear dynamic range of the stain is 476- and 48-fold for protein and DNA, respectively. A strong chelating agent such as ethylenediaminetetraacetic acid combined with a shift to basic pH (PH 8-10) elutes BPSA-Eu from the membrane. The reversible nature of the protein staining procedure allows for subsequent biochemical analyses, such as immunoblotting, lectin staining, and mass spectrometry.

Filamin translocation is an early endothelial cell inflammatory response to bradykinin: regulation by calcium, protein kinases, and protein phosphatases

Endothelial cell (EC) cytoskeletal proteins are one of the earliest primary targets of second messenger cascades generated in response to inflammatory agonists. Actin binding proteins, by modulating actin gelation-solation state and membrane-cytoskeleton interactions, in part regulate cell motility and cell-cell apposition. This in turn can also modulate interendothelial junctional diameter and permeability. Nonmuscle filamin (ABP-280), a dimeric actin-crosslinking protein, promotes orthogonal branching of F-actin and links microfilaments to membrane glycoproteins. In the present study, immunoblot analysis demonstrates that filamin protein levels are low in sparse EC cultures, increase once cell-cell contact is initiated and then decrease slightly at post-confluency. Both bradykinin and ionomycin cause filamin redistribution from the peripheral cell border to the cytosol of confluent EC. Forskolin, an activator of adenylate cyclase, blocks filamin translocation. Bradykinin activation of EC is not accompanied by significant proteolytic cleavage of filamin. Instead, intact filamin is recycled back to the membrane within 5-10 min of bradykinin stimulation. Inhibitors of calcium/calmodulin dependent protein kinase (KT-5926 and KN-62) attenuate bradykinin-induced filamin translocation. H-89, an inhibitor of cAMP-dependent protein kinase, causes translocation of filamin in unstimulated cells. Calyculin A, an inhibitor of protein phosphatases, also causes translocation of filamin in the absence of an inflammatory agent. ML-7, an inhibitor of myosin light chain kinase and phorbol myristate acetate, an activator of protein kinase C, do not cause filamin movement into the cytosol, indicating that these pathways do not modulate the translocation. Pharmacological data suggest that filamin translocation is initiated by the calcium/calmodulin-dependent protein kinase whereas the cAMP-dependent protein kinase pathway prevents translocation. Inflammatory agents therefore may increase vascular junctional permeability by increasing cytoplasmic calcium, which disassembles the microfilament dense peripheral band by releasing filamin from F-actin.

Immunolocalization of cytokeratin 19 in bovine and human pulmonary microvascular endothelial cells in situ

1. Immunocytochemical analysis of bovine and human lung sections revealed the presence of the 41 kD intermediate filament protein cytokeratin 19 in microvessel and subpleural lymphatic endothelial cells as well as the mesothelial cell layer of the lung visceral pleura. 2. Cytokeratin 19 was expressed by human and bovine pulmonary microvessels with diameters ranging from 5 to 50 microns. 3. Cytokeratin 19 was also found in microvessels of the rete mirabile, an oxygen exchange organ of the eel. 4. Immunoperoxidase electron microscopy demonstrated cytokeratin 19 associated with the lateral membranes of adjacent bovine alveolar capillary endothelial cells.

Possible mechanism(s) for permeability recovery of venules during histamine application

Histamine is known to cause a substantial increase in the permeability of venules to both water and proteins. However, this increase is transient, i.e., the initially elevated permeability returns toward control levels, or "recovers," even during continuous histamine stimulation. In this investigation, we attempted to identify the possible chemical signal(s) initiating the permeability recovery process in single venules of rat mesentery. Specifically, we tested whether histamine's binding to H2 receptors and/or the production of prostacyclin by endothelial cells was involved in this process. To achieve this aim, the time course of endothelial cells was involved in this process. To achieve this aim, the time course of histamine-induced changes in permeability to alpha-lactalbumin was measured in the presence of H2 receptor antagonist (cimetidine) or of prostacyclin synthetase inhibitor (tranylcypromine), respectively. Permeability of individually perfused microvessels was measured using fluorescence microscopy. The results demonstrated that permeability recovery was not affected by the H2 receptor antagonist but was suppressed or even abolished by the prostacyclin synthesis inhibitor. Therefore, these results suggest that the production of prostacyclin by endothelial cells might serve as one chemical signal to initiate the permeability recovery process, whereas histamine's binding to H2 receptors is not involved in this phenomenon.