In vitro effects of endotoxin on bovine and sheep lung microvascular and pulmonary artery endothelial cells

Oxygen radicals--an important mediator of sepsis and septic shock

There is considerable evidence to implicate aggressive species of oxygen in the pathogenesis of organ dysfunction consequent to sepsis and septic shock. The inflammatory process appears to participate ubiquitously in this setting. A characteristic of inflammation is the involvement of activated neutrophils and their generation of aggressive oxygen species. Such species may both directly injure cells proximal to the oxidant generating cells, and may inactivate any proteolytic mechanisms normally protective against proteolytic injury caused by neutrophil elastase and other proteolytic enzymes released during inflammation. The offending agent in sepsis is most commonly envisioned as bacterial lipopolysaccharide, or endotoxin. Infusion of endotoxin into animals can reproduce much of the pathophysiology of sepsis and septic shock. In addition, administration of endotoxin to cultured cells, particularly endothelial cells, can cause responses consistent with a sequence of events that occurs in intact animals and humans. In both experimental models, it appears that aggressive oxygen species are important actors in the scenario eventuating in cell or organ injury. Of importance, the toxic consequences of these free radicals probably occurs in relatively protected spaces, including microenvironments created by close adherence between inflammatory cells and endothelial cells and the cell interior. For those reasons, the potential for antioxidants as therapy should include consideration of the volume of distribution of such substances. It is probably important that antioxidants access excluded spaces including cell interiors in order to have their maximum effect in this setting. We have studied ina preliminary way the effects of n-acetyl-cysteine, a highly permeable free radical scavenger and anti-oxidant, in patients with established ARDS.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure function correlates in the pulmonary vasculature during acute lung injury and chronic pulmonary hypertension

Arteries, veins, and capillaries comprise the pulmonary vasculature. Three structural types of artery and vein are identified, the most muscular vessels being the largest. For example, arteries that accompany the preacinar arteries are muscular in structure while those within the acinus may be either, muscular, partially muscular or non-muscular. These small intra-acinar arteries contribute much to the hemodynamic behavior of the lung. Pulmonary edema results from damage to the capillary endothelium while chronic pulmonary hypertension is characterized by structural alterations in the pulmonary arteries. Correlation of the structural and functional changes of chronic pulmonary hypertension suggest that the increases in medial and adventitial thickness of the muscular preacinar arteries are secondary to the onset of this disease, while the changes in the peripheral arteries--appearance of muscle in smaller intra-acinar arteries than normal and reduction in arterial volume--contribute to the rise in pulmonary artery pressure and pulmonary vascular resistance. Such correlations of structure and hemodynamic measurements demand that the lung be fixed in a simple and standardized manner. Available methodology to evaluate the structural changes that occur during the development of pulmonary edema and chronic pulmonary hypertension are described.

Blood-brain barrier alterations in bacterial meningitis: development of an in vitro model and observations on the effects of lipopolysaccharide

To further examine the effects of purified Haemophilus influenzae type b lipopolysaccharide (LPS) on blood-brain barrier permeability, we have developed an in vitro model of the BBB. Microvascular endothelial cells were isolated from rat cerebral cortices by enzymatic digestion, dextran centrifugation, and separation on percoll gradients. The cells were determined to be endothelial in origin by positive fluorescent staining for Factor VIII-related antigen and the ability to take up acetylated low density lipoproteins, and their cerebral origin by the formation of junctional complexes in vitro. Cells were seeded onto semipermeable polycarbonate filters and permeability assessed by measuring traversal of radioactive albumin across the monolayer. Treatment of the cells with LPS at concentrations of 1.0 microgram/ml and 0.1 microgram/ml for 4 h led to statistically significant increases in albumin permeability of 4.6% (P = 0.001) and 5.6% (P less than 0.001), respectively, without evidence of cell death as assessed by release of lactate dehydrogenase into the media. These results indicate that LPS significantly increases albumin permeability across a monolayer of cerebral microvascular endothelial cells in the absence of host inflammatory cells. Future studies on the effects of LPS on intracellular regulation will determine the mechanisms responsible for these alterations.

Primed stimulation of isolated perfused rabbit lung by endotoxin and platelet activating factor induces enhanced production of thromboxane and lung injury

Bacterial sepsis often precedes the development of the adult respiratory distress syndrome (ARDS) and bacterial endotoxin (LPS) produces a syndrome similar to ARDS when infused into experimental animals. We determined in isolated, buffer-perfused rabbit lungs, free of plasma and circulating blood cells that LPS synergized with platelet activating factor (PAF) to injure the lung. In lungs perfused for 2 h with LPS-free buffer (less than 100 pg/ml), stimulation with 1, 10, or 100 nM PAF produced transient pulmonary hypertension and minimal edema. Lungs perfused for 2 h with buffer containing 100 ng/ml of Escherichia coli 0111:B4 LPS had slight elevation of pulmonary artery pressure (PAP) and did not develop edema. In contrast, lungs exposed to 100 ng/ml of LPS for 2 h had marked increases in PAP and developed significant edema when stimulated with PAF. LPS treatment increased capillary filtration coefficient, suggesting that capillary leak contributed to pulmonary edema. LPS-primed, PAF-stimulated lungs had enhanced production of thromboxane B2 (TXB) and 6-keto-prostaglandin F1 alpha (6KPF). Indomethacin completely inhibited PAF-stimulated production of TXB and 6KPF in control and LPS-primed preparations, did not inhibit the rise in PAP produced by PAF in control lungs, but blocked the exaggerated rise in PAP and edema seen in LPS-primed, PAF-stimulated lungs. The thromboxane synthetase inhibitor dazoxiben, and the thromboxane receptor antagonist, SQ 29,548, similarly inhibited LPS-primed pulmonary hypertension and edema after PAF-stimulation. These studies indicate that LPS primes the lung for enhanced injury in response to the physiologic mediator PAF by amplifying the synthesis and release of thromboxane in lung tissue.

Lipid metabolism and signal transduction in endothelial cells

Endothelial cells have the capacity to metabolize several important lipids; this includes the ability to store and then metabolize arachidonate, as well as the capacity to synthesize platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine). Arachidonate is predominantly metabolized via cyclooxygenase to PGI2 although the spectrum of prostaglandins may vary depending upon the source of the endothelial cell. Biosynthesis of eicosanoids and PAF are likely to be an important physiologic function of the endothelial cell as these potent lipids appear to have a role in maintaining vascular tone and mediating interactions of the endothelium with circulating inflammatory cells. In addition to production of eicosanoids and PAF, endothelial cells metabolize exogenous arachidonate and arachidonate metabolites and other fatty acids such as linoleate to bioactive compounds (HODEs). There is also evidence that small amounts of arachidonate are metabolized via a lipoxygenase. The physiologic significance of these minor lipid pathways is not known at this time. Production of eicosanoids and PAF is not a constitutive function of the endothelial cell. Lipid biosynthesis by endothelial cells is one component of the early activation response that occurs in response to stimulation with pro-inflammatory and vasoactive hormones or to pathologic agents such as oxidants and bacterial toxins. A central mechanism for activation of the relevant pathways is a rise in cellular calcium concentrations that can be mediated by hormone-receptor-binding or by direct permeabilization of the cell membrane to calcium (Fig. 3). Regulatory mechanisms distal to the calcium signal are unknown, but current evidence suggests that calcium directly or indirectly activates phospholipases that release arachidonate from phospholipids and hydrolyze a specific phospholipid to the immediate precursor of PAF. There is evidence that protein kinase C may, in part, regulate this process, but the role of other potential regulatory components, such as other protein kinases or G-proteins is not known. As noted above, the most direct mechanism for initiation of PAF biosynthesis and arachidonate release would be activation of a phospholipase A2 as shown in Fig. 3. Activation of other phospholipases (e.g. phospholipase C) may contribute to the total amount of arachidonate released, although the magnitude of that contribution is not yet known. In addition to generation of PAF and eicosanoids, activation of endothelial cell phospholipases generates second messengers that are important in intracellular signaling (Fig. 4). Activation of phospholipase C, in response to hormonal stimulation, generates diacylglycerol and inositol phosphates from phosphatidylinositol. Each of these is a potent intracellular second messenger.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of a prokaryotic gene in cultured lung endothelial cells after lipofection with a plasmid vector

Transfection of cultured cells with functioning foreign genes can be a powerful tool for delineating mechanisms controlling gene expression and for manipulating cellular synthetic machinery. We transfected cultured bovine pulmonary artery endothelial cells with a plasmid (pRSVCAT) containing the prokaryotic gene, chloramphenicol acetyltransferase (CAT), driven by a Rous sarcoma virus (RSV) promoter. Transfection was accomplished by binding the plasmid DNA to specially synthesized cationic liposomes and incubating cell monolayers with the liposome-DNA complex (a process called lipofection). We found marked CAT expression in endothelial cells by 24 h after lipofection (complete chloramphenicol acetylation in a 4-h assay incubation with less than 0.1 mg cell protein). Marked CAT expression persisted after splitting the cells 1:2 at 6 days after lipofection. Detectable CAT activity was present 14 days after lipofection following two 1:2 splits of the cells. CAT expression was related to the quantity of plasmid DNA used for lipofection; 1.0 micrograms DNA per 60-mm dish of cells resulted in less CAT activity at 48 h than did 5 or 10 micrograms DNA per dish. Ten micrograms of DNA-liposome complex per dish caused substantial numbers of endothelial cells to detach from the dish, but little cytotoxic effect was seen with 5 or 1 micrograms DNA-liposome complex per dish. This simple, highly efficient method for introducing functioning foreign genes into cultured endothelial cells will permit a broad range of studies of molecular mechanisms of endothelial cell function and studies of the consequences of highly specific modifications in protein synthesis on endothelial responses.

Human recombinant interleukin 2-activated sheep lymphocytes lyse sheep pulmonary microvascular endothelial cells

Administration of lymphokine-activated killer (LAK) cells in combination with interleukin 2 (IL-2) has been effective in reducing tumor mass in humans, but has been accompanied by significant toxicity. We used a chronic awake sheep model to investigate the cause of the vascular leak syndrome associated with IL-2 administration. Sheep repeatedly infused with human recombinant IL-2 (hrIL-2) developed mild pulmonary hypertension, systemic hypotension, acidemia, hypoxemia, and increased flow of protein rich lung lymph. We hypothesized that LAK cells may damage lung endothelium in vivo and cause increased lung vascular permeability. Sheep peripheral blood and lung lymph lymphocytes incubated in vitro with hrIL-2 generated cytotoxic activity for human K-562 cells and sheep pulmonary microvascular endothelial cells. In addition, cytotoxic effector cells were isolated from the peripheral blood of a sheep which had received hrIL-2. These observations suggest that LAK cells possess the ability to damage endothelial cells and may contribute to an increased pulmonary vascular permeability observed following hrIL-2 infusion in sheep.

Cellular events in alveolitis and the evolution of pulmonary fibrosis

"Alveolitis", as opposed to "pneumonia" sensu strictiori, is a term used to denote diffuse inflammatory changes of the pulmonary parenchyma, excluding those that result from local bacterial, fungal or other extracellular microbial growth. The various types of alveolitis are classified according to their histological characteristics and range from "luminal phagocytic" or "mural lymphoplasmacellular" and "exudative" to "fibrosing" alveolitis. In this overview, various exogenous and endogenous causes of different types of alveolitis, and the cellular events in their pathogenesis are briefly discussed to illustrate the complex mechanisms involved. Particular emphasis is placed on the possible transition from diffuse exudative to fibrosing alveolitis. It appears that pulmonary fibrosis, which is usually patchy rather than truly diffuse, does not have a uniform pathogenesis. Besides the possibility of a certain degree of a diffuse fibrosis three major pathways are evident: (1) granulation tissue budding into alveolar lumina (luminal fibrosis) (2) exudate incorporation into alveolar walls (mural fibrosis) and--at least equally important--(3) so-called collapse (atelectatic) induration (obliterative-interseptal fibrosis), a process that has largely been neglected so far.