Circulating Blood Components Research Articles

CD40 signaling in vascular cells: a key role in atherosclerosis?

Atherosclerosis is one of the most prevalent fatal diseases in Western societies, and results from an intricate interplay between diverse factors such as lipid metabolism, blood coagulation elements, cytokines, hemodynamic stress, and behavioral risk factors. Atherosclerotic lesions are characterized by the infiltration of immune competent cells such as macrophages and T-lymphocytes, the proliferation of intimal cells of the arterial wall, the accumulation of lipids and the deposition of extracellular matrix components. For some years, endothelial cells, smooth muscle cells, and macrophages have been accorded crucial roles in the process of atherosclerosis. The mechanisms by which these cells contribute to atherosclerosis include augmented expression of adhesion molecules, as well as secretion of proinflammatory cytokines, matrix metalloproteinases, and tissue factor within human and experimental atheroma. Much evidence supports the role of tissue factor in inciting the thrombosis that causes most acute coronary syndromes. Macrophage content and expression of tissue factor correlate with rupture and instability of the atherosclerotic plaque. Matrix metalloproteinases can digest the plaque's extracellular matrix, and thus impair its stability. Plaque rupture exposes circulating blood components to the tissue factor-rich lipid-core, inciting thrombosis. Despite the increasing appreciation that atherogenesis involves participation of inflammatory pathways within cellular interactions, mediators of local communication between the major cell types within atherosclerotic plaques remain incompletely defined. By early appearance, activated T-cells may act as the orchestrator of atherogenesis. Both soluble and contact-dependent mediators from T-cells may be crucial in the development of this prevalent disease. Recent reports have helped explain some of these questions by pointing to a role of contact dependent interaction between CD40 and CD40 ligand (CD40L, renamed CD154) as a stimulus for atheroma-associated cells. We and others have recently showed that activated T-lymphocytes within the atherosclerotic vessel wall express the CD40 ligand surface molecule, known to play a major role in several immunological pathways. In addition to activated T-lymphocytes, functional CD40 and CD40L are coexpressed by human vascular endothelial cells, smooth muscle cells and human macrophages in vitro as well as in situ in human atherosclerotic lesions. Recent studies indicate that CD40L activates atheroma-associated cells by promoting the expression of molecules thought to be involved in atherosclerosis, such as adhesion molecules, cytokines, matrix metalloproteinases, and tissue factor. Thus, CD40 ligation on these vascular wall cells may promote mononuclear cell recruitment, participate in the weakening of the plaque and set the stage for thrombosis, mechanisms of crucial importance in the process of atherosclerosis. The involvement of the CD40 signaling pathway may play major roles during atherogenesis by regulating antigen-specific T-cell responses to yield activation instead of tolerance, and the presence of functional CD40L on non-leukocytic cells associated with atherosclerotic lesion indicates a novel T-cell-independent route of inflammatory activation, a now well recognized component of atherogenesis. These findings establish a possible crucial role for CD40-CD40L interactions in a prevalent human disease.

X-irradiated vascular endothelium activates circulating blood components through exocytosis of membranous organelles containing preformed proteins

X-irradiated vascular endothelium activates circulating blood components through exocytosis of membranous organelles containing preformed proteins

Role of circulating blood components and thromboxane in anaphylactic vasoconstriction in isolated canine lungs.

We determined the roles of circulating blood components and chemical mediators in anaphylactic vasoconstriction and microvascular permeability during Ascaris suum antigen-induced anaphylaxis in isolated canine lungs. Either the right or left lower lobe served as the control lung, which was perfused with autologous blood, and the contralateral lobe from the same dog was examined for the effect of albumin Krebs-Henseleit solution (Krebs) or of blockers of various vasoconstrictors with blood perfusion. Pulmonary vasoconstriction occurred after injection of the antigen (15 mg) in both the blood- and Krebs-perfused lungs. However, the percent change of peak pulmonary vascular resistance in the Krebs-perfused lungs tended to be greater than that in the blood-perfused lungs (689.9 +/- 289.3 and 389.3 +/- 171.9%, respectively). This increased peak pulmonary vascular resistance was attenuated similarly by pretreatment with indomethacin (1.1 x 10(-4) M; cyclooxygenase inhibitor), AA-2414 (10(-5) M; thromboxane-receptor antagonist), or a combination of TCV-309 (10(-5) M; platelet-activating factor-receptor antagonist), diphenhydramine (1.7 x 10(-4) M, histamine H1-receptor antagonist), and indomethacin but not by pretreatment with TCV-309 or diphenhydramine alone. The filtration coefficient, an index of vascular permeability, did not change significantly at 15 or 60 min after the antigen in all groups. These findings suggest that anaphylactic vasoconstriction in the isolated canine lung is independent of circulating blood components. Thromboxane is the major mediator for the anaphylactic vasoconstriction. Anaphylaxis does not increase pulmonary vascular permeability in isolated canine lungs.

Endotoxin stimulates the expression of group II PLA2 in rat lung in vivo and in isolated perfused lungs.

Injection of endotoxin in vivo leads to increased phospholipase A2 (PLA2) activity in the lung, but neither the type(s) of PLA2 involved nor the importance of blood components and/or different inflammatory cytokines has been clarified. In the present study, injection of endotoxin in rats caused increased lung levels of group II PLA2, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-1 beta mRNA, while group I PLA2 mRNA levels were unaffected. The augmented group II PLA2 mRNA levels corresponded to a rise in membrane-associated PLA2 enzymatic activity that was inhibited by rutin, an inhibitor of group II PLA2. In blood-free, salt-perfused lungs, addition of endotoxin to the perfusate caused elevated group II PLA2, TNF-alpha, and IL-1 beta mRNA levels and release of PLA2 and TNF-alpha activity into the perfusate, and when instilled intratracheally, endotoxin caused increased PLA2 activity in the lung tissue. It is concluded that 1) endotoxin stimulates group II PLA2, but not group I PLA2, in rat lung cells, 2) this stimulation is accompanied by increased expression of TNF-alpha and IL-1 beta, and 3) endotoxin-induced PLA2 activation and cytokine production in the lung are not dependent on circulating blood components.

FragminTM (LMWH) vs heparin for anticoagulation during in vitro recycling of human blood in cardiopulmonary bypass circuits

Low-molecular-weight heparin (LMWH) (Fragmin) vs heparin was studied in vitro in order to investigate its antithrombotic efficacy in the isolated thrombogenic link of cardiopulmonary bypass (CPB). Fresh human blood (400 ml) with various dosages of the anticoagulant was recycled in a CPB circuit for 120 min. The standard dosage of heparin (1,500 IU, n = 6) was compared with a lower dosage (1,000 IU, n = 3) and several dosages of Fragmin (IU anti-FXa): 750 (n = 1), 1,500 (n = 3), 2,100 (n = 4) and 2,500 (n = 3). Clotting occurred in three Fragmin experiments at dosages of 750, 1,500 and 2,100 IU. This was associated with short activated clotting time (ACT) and activated partial thromboplastin time (aPTT) but was independent of the levels of anti-FXa, FVIII, von Willebrand factor and prothrombin complex. It was concluded that at least twice the dose of Fragmin (anti-FXa), compared with heparin, was required, suggesting that thrombin inhibition is crucial for the antithrombotic efficacy of heparin in CPB circuits. Absence of fibrinolytic markers suggests that the well known enhancement of fibrinolysis often seen during CPB, is not due to heparin interaction with normally circulating blood components, but rather to interaction with the vessel walls or to the surgical trauma itself.

Thrombin-induced endothelial cell dysfunction.

Endothelium is a multifunctional organ which can directly influence circulating blood components as well as other cells within the vessel wall. The clotting enzyme thrombin, generated at the surface of damaged endothelium, induces blood coagulation but also exerts a variety of functional effects on the endothelium itself. Thrombin acts on endothelial cells to stimulate synthesis and release of various agents, such as inflammatory mediators, vasoactive substances and growth factors. It causes leukocyte adhesion to the endothelium by triggering expression of adhesion molecules on the cell surface and causes disruption of endothelial permeability properties. The majority of thrombin effects on endothelial cells are mediated by its receptor and require its lytic activity. Differences have been observed among the response to thrombin of endothelial cells of different origin. In general microvascular endothelial cells appear to be particularly sensitive to this enzyme. Thrombin induced microvascular dysfunction can have pathological consequences and contribute to organ reactions to inflammation and ischaemia.

Seminars in thrombosis, thrombolysis, and vascular biology. 6. Procoagulant states.

Under normal physiologic conditions, blood flows freely within the coronary arteries and peripheral vasculature, providing oxygen and essential nutriments to vital organs and metabolically active tissues. The natural thromboresistant properties of the vascular endothelium and circulating blood components provide the ideal environment for this fundamental, life-sustaining process. While hemostasis is a vital defense mechanism, preventing blood loss and ensuring rapid vessel repair, nonphysiologic thrombosis or 'hemostasis in the wrong place' may impair blood flow enough to cause debilitating or life-threatening tissue damage. Procoagulant (prothrombotic) states promote nonphysiologic thrombosis and reflect one or more significant abnormalities in either the vessel wall, circulating blood, or plasma coagulation components themselves. Although a heightened thrombotic tendency may be the end result of a focal or systemic pathologic process, in either case, thromboembolic events involving the cardiovascular system may ensue.

Interaction of platelets and purified collagens in a laminar flow model

Damage to the endothelial surface of the vessel wall can result in exposure of circulating blood components to collagen and other subendothelial structures. Collagen types I, III, IV, and V have been demonstrated in the vessel wall by chemical and immunohistological methods; type V is thrombin-sensitive, and is present on the endothelial cell surface. In an earlier study using a rocking model, both unstimulated and ADP-induced platelet adherence was (1) reduced on wells coated with type V collagen in comparison to uncoated wells; and (2) increased on plastic surfaces coated with types III and IV collagen in comparison to those coated with type V collagen. The present study was designed to determine the effect of erythrocytes and shear rate on platelet adherence to these purified collagen types in a laminar flow system. With platelet-rich plasma, adherence of labeled platelets was much lower in the laminar flow system compared with the rocking model. Erythrocytes significantly enhanced platelet adherence to surfaces that were untreated or absorbed with collagen types I, III, and IV. However, this enhancement was not seen in the presence of type V collagen. These studies provide additional evidence for the selectively nonthrombogenic nature of type V collagen.

Adverse effects of butyl benzyl phthalate on the reproductive and hematopoietic systems of male rats

A 14-day dietary study was conducted in adult, male, Fischer 344 rats at levels of 0.0, 0.625, 1.25, 2.5 and 5.0% butyl benzyl phthalate (BBP) to evaluate potential effects of this plasticizer on the male and reproductive and hematopoietic systems. Total body, thymus, testis, epididymis, prostate and seminal vesicle weights were reduced in the 2.5% and 5% BBP dose groups, while pituitary weight was unaffected. Histological evaluations revealed dose-dependent atrophy of the testis, prostate and seminal vesicles at 2.5% and 5%, atrophy of the thymus and epididymis at 5%, and the presence of immature sperm cells in the tubular lumens and necrosis of the tubular epithelium in the epididymis at 2.5% and 5% BBP. Plasma testosterone concentration was decreased at 5%, while follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations were increased at 2.5% and 5.0% BBP. The circulating components of blood, and clotting times (prothrombin time, activated partial thromboplastin time), were unaffected although bone marrow cellularity was reduced at 2.5% and 5%. Changes in non-reproductive organs included enlargement of liver and kidneys, thymic atrophy and associated morphological abnormalities in these organs. These data indicate a direct toxic effect of BBP on the testis with secondary effects on other reproductive organs. Pituitary and hypothalamic responses did not appear to be affected. The reduced bone marrow cellularities suggest that prolonged exposures to BBP could affect circulating blood components or compromise clotting ability.

Toxic responses to acute, subchronic, and chronic oral administrations of monochlorobenzene to rodents.

Acute (single exposure), 14-d repeated exposure, 91-d subchronic, and 103-wk chronic toxicity studies of orally administered (gavage, in corn oil) monochlorobenzene were conducted in male and female Fischer-344 rats and B6C3F1 hybrid mice. A single exposure to 4000 mg/kg was lethal to male and female rats, while a single exposure to a dose as low as 1000 mg/kg was lethal to mice. Fourteen daily exposures to 1000 mg/kg caused death in rats of both sexes, but neither survival nor clinical health were compromised at 500 mg/kg in rats or mice. In the 91-d studies, wherein monochlorobenzene was administered once daily, 5 d/wk, survival was reduced by doses of 500 mg/kg and higher in rats, and by doses of 250 mg/kg and higher in mice. Dose-dependent necrosis of the liver (hepatocytes), degeneration or focal necrosis of the renal proximal tubules, and lymphoid or myeloid depletion of the spleen, bone marrow, and thymus (mild to severe) were produced by doses of 250 mg/kg or greater of monochlorobenzene in both sexes of rats and mice, although the incidences of these lesions varied considerably by sex and species. Consistent changes in the circulating blood components were not observed, but a mild porphyrinuria was detected at the higher doses. No toxic effects were observed at doses of 125 mg/kg or less. In the 2-yr studies, wherein monochlorobenzene was administered once daily, 5 d/wk, doses of 30 or 60 mg/kg in male mice and 60 or 120 mg/kg in female mice and male and female rats did not produce any evidence of toxicity. Doses of 60 or 120 mg/kg caused slight (statistically significant at 120 mg/kg; p less than 0.05) increases in the frequencies of male rats with neoplastic nodules of the liver. Increased tumor frequencies were not observed in female rats or in male or female mice receiving monochlorobenzene.

Effect of low levels of nitrogen dioxide inhalation on endogenous retrovirus gene expression

Cellular RNA prepared from various tissues of mice exposed to ambient levels of nitrogen dioxide (NO 2) for 1 to 20 weeks was examined for evidence of changes in the level of expression of endogenous retrovirus genes. Two strains of mice were used: low retrovirus expressor (Swiss Webster strain) and high retrovirus expressor (AKR strain). Low expressor mice were exposed to 0.8 ± 0.05 ppm and the high expressor mice to 0.3 ± 0.05 ppm NO 2. Among the tissues examined (lung, kidney, thymus, and spleen) of the low expressor mice only the spleen showed a significant elevation of the level of endogenous viral RNA in response to the NO 2 exposure. The elevation did not persist throughout the study; it was detected during the 1st and 18th weeks of exposure, whereas the viral RNA levels were near normal at periods in between. Similarly, the high expressor mice appeared to react to NO 2 exposure with the spleen showing enhanced retrovirus gene expression during the 1st, 8th, 12th, and 15th weeks of exposure. Measurements at the end of the 2nd and 20th weeks of study, however, showed comparable levels in spleens of the exposed and control mice. Although the activity of the virus genes is naturally elevated in the thymic tissue of AKR mice, the levels of viral RNA or the incidence of thymic lymphoma were not significantly altered by exposure to 0.3 ppm NO 2. The observed alterations of genetic expression in the splenic tissue of two different strains of mice, together with the fact that the spleen is closely interrelated with circulating blood components, support the emerging notion that the spleen is a target organ for the effects of inhalation of ambient levels of NO 2.