Pierre Sirois

Growth regulatory properties of endothelins

Endothelins are produced by endothelial and epithelial cells, macrophages, fibroblasts, and many other types of cells. Their receptors are present in numerous cells, including smooth muscle cells, myocytes, and fibroblasts. Evidence now suggests that the three isoforms of endothelins (ET-1 and the other two related isopeptides, ET-2 and ET-3) regulate growth in several of these cells. Endothelin-1 influences DNA synthesis, the expression of protooncogenes, cell proliferation, and hypertrophy. The participation of ET in mitogenesis involves activation of multiple transduction pathways, such as the production of second messengers, the release of intracellular pools of calcium, and influx of extracellular calcium. Moreover, ET-1 acts in synergism with various factors, such as EGF, PDGF, bFGF, TGFs, insulin, etc., to potentiate cellular transformation or replication. Several of these factors may in turn stimulate the synthesis and/or the release of endothelins. The production and release of endothelins are also increased in acute and chronic pathological processes, e.g., atherosclerosis, postangioplastic restenosis, hypertension, and carcinogenesis. It is postulated that endothelins act in a paracrine/autocrine manner in growth regulation and play an important role mediating vascular remodeling in some cardiovascular diseases. The present review analyses the implication of endothelins (ET-1, -2, and -3) in physiopathology related to their growth regulatory properties.

Leukotriene B4 induces human suppressor lymphocytes

Leukotrienes C 4 , D 4 and E 4 are the main bioactive components of slow-reacting substance of anaphylaxis, while leukotriene B 4 has proven to be a potent chemoattractant for neutrophils. We report that LTB 4 is also a potent inducer of suppressor cell activity at concentrations as low as 1 × 10 −14 M. The induced suppressor cells are T lymphocytes which do not require proliferation to exert their activity and which are sensitive to irradiation at 2000 rads. We suggest that LTB 4 may play an important role in immuno-regulation during hypersensitivity reactions.

Leukotriene B4 augments human natural cytotoxic cell activity

We have recently shown that leukotriene B4 (LTB4) activates T lymphocytes to become suppressor cells. We now report that LTB4 also augments human natural cytotoxic cell activity against target cells infected with herpes simplex virus. This activity is partially inhibited by the lipoxygenase inhibitor nordihydroguaiaretic acid and the thromboxane synthetase inhibitor OKY-1581, but is augmented by indomethacin. We suggest that LTB4 may play a role in early host defense responses during inflammatory and infectious disease processes.

Transformation of arachidonic acid in leukocytes. Isolation and structural analysis of a novel dihydroxy derivative.

Abstract A suspension of mixed peripheral blood leukocytes was incubated with arachidonic acid. After ether extraction and silicic acid fractionation of the products, the fraction containing the mono- and dihydroxy derivatives of arachidonic acid was further analyzed by high pressure liquid chromatography on silica gel and octadecyl silica (reversed-phase) columns. A previously undescribed metabolite was detected and isolated in pure form. The compound co-chromatographed with leukotriene B4 on octadecyl silica but was eluted earlier than leukotriene B4 from silica gel columns. Ultraviolet spectrophotometry, gas chromatography-mass spectrometry, ozonolysis and steric analysis indicated that the new metabolite was the 5S,12S-dihydroxy-6,8,10,14-icosatetraenoic acid. The yield of the novel dihydroxy acid was 1 to 4% of the added substrate. The new metabolite showed less than 1% of the myotropic activity of leukotriene B4 on the guinea pig lung parenchymal strip.

Pharmacological activity of leukotrienes A4, B4, C4 and D4 on selected guinea-pig, rat, rabbit and human smooth muscles

The myotropic activity of leukotrienes A4, B4, C4, D4 and histamine has been evaluated on selected smooth muscle preparations. LTA4, B4, C4 and D4 were several times more potent than histamine on the guinea-pig lung parenchymal strip, while on the guinea-pig trachea, LTB4 was less active. The guinea-pig ileum either in segments or in strips of longitudinal muscles responses well to LTC4, LTD4 and histamine but not to LTA4 and LTB4. Rat and rabbit lung parenchymal strip showed very little sensitivity for leukotrienes whereas human parenchymal strips and bronchi were nearly as sensitive as the guinea-pig lung.

The action of leukotriene B4 (LTB4) on the lung

The actions of leukotriene B4 (LTB4), a member of a newly discovered pathway of metabolism of arachidonic acid, were investigated both on the guinea-pig perfused lung preparation and on the parenchymal strip and compared to histamine and Slow Reacting Substance of Anaphylaxis (SRS-A). LTB was prepared from human polymorphonuclear leukocytes, extracted and purified by chromatography (Silicic acid and HPLC) and its purity was determined by gas chromatography and mass spectrometry. LTB4 is three times more potent than histamine (molar concentration) to contract the parenchymal strips and the contraction to LTB4 as well as to SRS-A lasted longer. The contraction to LTB4 is blocked by indomethacin (20 micrograms/ml), reduced by polyphloretin phosphate (50 micrograms/ml) and unaffected by FPL-55712 (1 micrograms/ml). Following its injection in the pulmonary artery of a perfused lung, LTB4 (1 microgram) induced the release of RCS (Rabbit Aorta Contracting Substance: a mixture of prostaglandins and thromboxanes) which can be abolished by indomethacin (1 microgram/ml). These findings suggest (a) that in the lung, LTB4 is a myotropic agent three times more powerful than histamine (b) that LTB4 stimulated a receptor which is different of histamine of SRS-A receptors, and (c) that its contractile action in the lung is mediated by prostaglandins and thromboxanes.

Evidence for a mediator role of thromboxane A2 in the myotropic action of leukotriene B4 (LTB4) on the guinea-pig lung

The mechanism of action of LTB4 has been investigated on the guinea-pig lung parenchymal strip. Mepacrine (20 microgram/ml), an inhibitor of phospholipase A2, abolished the action of LTB4 on parenchymal strips. Eicosatetraynoic acid (10 microgram/ml) and BW755C (40 microgram/ml) which are inhibitors of cyclooxygenase and lipoxygenase pathways, produced a marked inhibition of the lung strip contraction to LTB4. Similarly, aspirin (30 micrograms/ml) and flufenamate (1 microgram/ml) showed a strong inhibition of the contraction of parenchymal strips to LTB4; these results suggested that cyclooxygenase products mediate the action of LTB4. The response to LTB4 was unaffected by 15-hydroperoxyeicosatatraenoic acid (15-HPETE; 1 microgram/ml) while L8027 (25 ng/ml) reduced the contraction by 50%, suggesting that thromboxane A2 rather than prostacyclin was involved. Since parenchymal strips do not appear to be very sensitive to PGF2 alpha, PGE2 and the endoperoxides, and since effluents from LTB4-treated lungs produced contractions of lung strip and rabbit aorta which were reduced after 5 min. at 25 degrees, thromboxane A2 was postulated to mediate the lung effect of LTB4. The release of thromboxane B2 (TxB2) from lungs stimulated with LTB4 was confirmed by gas-chromatography-mass spectrometric (GC-MS) analyses.

Asbestos-induced lung injury in the sheep model: The initial alveolitis

In order to study the cellular and biochemical changes in early asbestosis, three groups of sheep were repeatedly exposed to intratracheal instillations of either saline (controls), low doses of UICC chrysotile asbestos (LD), or high doses of the fibers (HD) until an alveolitis was observed in all HD sheep during the twelfth month of exposure. All sheep were studied bimonthly by transbronchial lung biopsy (LB), bronchoalveolar lavage (BAL), pulmonary function tests (PFT), and chest roentgenograms (CXR). While LBs of the HD sheep demonstrated large accumulations of monocyte-macrophages in the alveolar and interstitial spaces, those of controls and LD sheep did not. In BAL, there was no difference in total and differential cell counts between groups, but the BAL lymphocyte proliferative capacity was clearly depressed in all asbestos-exposed sheep. In the BAL supernatant, total proteins (mainly albumin, beta + gamma globulins) and lactate dehydrogenase were significantly elevated in the HD group only. This alveolitis was associated with a fall in vital capacity, lung compliance, diffusing capacity, and arterial PO2. Abnormalities on CXR appeared 3 months later. Thus, the cellular and biochemical features of early asbestosis are clearly distinct from those reported in idiopathic pulmonary fibrosis.

Consequences of alteration in capillary permeability

In this review paper, three aspects related to alteration in capillary permeability, based on a series of recent observations from this laboratory, are examined. Firstly, the determinants of capillary extravasation, which include pre- and post-capillary resistances in different microcirculation networks, as well as endothelial permeability per se, are described with particular reference to the heterogeneous character of both regulatory components, reported by this and other groups. Secondly, the endothelium-interstitium relationship, responsible in part for the maintenance of the interstitial compartment physicochemical characteristics, is introduced as an important factor in regulating the traffic of vital nutrients delivered to the cell mass, and the removal of waste products from the cellular compartment to the microcirculation, for ultimate excretion. Examined in this manner, it appears that modulation of capillary permeability is essential for the maintenance of cellular life, yet the neurohumoral mechanisms involved in the control of microcirculation networks are just starting to be identified. A number of morbid conditions characterized by multiorgan involvement exhibit a common pathophysiological denominator which involves endothelium-interstitium relationships, as illustrated in experimental animal models of arterial hypertension, diabetes mellitus, heart failure, and degenerative renal diseases. Enhanced capillary permeability associated with local interstitial edema in specific organs, such as the heart and the kidney, in arterial hypertension and diabetes mellitus, as well as decreased permeability in peripheral tissues, such as the skeletal muscle and the skin, in congenital cardiomyopathy, have been documented. It is likely that alteration in the characteristics of interstitial matrix composition contributes to target organ damage in these examples of systemic disorders from different etiologies. Thirdly, the recent identification of autocoids and hormones involved in the direct and indirect control of capillary permeability has led to the development of pharmacological tools capable of modulating pre- and post-capillary vascular tonus, as well as endothelial permeability. Angiotensin II antagonism, bradykinin B1-receptor inhibition, and modulation of eicosanoid production, in particular thromboxane A2, are associated in some of the above-described disorders, with normalization of capillary permeability defects, and occasionally with improvement in organ function. The eventual development of agents capable of directly controlling the physicochemical characteristics of the interstitial matrix should be of interest, not only for preventing the development of irreversible matrix structural alterations but also for facilitating the traffic of metabolites between capillaries and the cell mass of vital organs.

The kinin system mediates hyperalgesia through the inducible bradykinin B1 receptor subtype: evidence in various experimental animal models of type 1 and type 2 diabetic neuropathy.

Abstract Both insulin-dependent (type 1) and insulin-independent (type 2) diabetes are complex disorders characterized by symptomatic glucose intolerance due to either defective insulin secretion, insulin action or both. Unchecked hyperglycemia leads to a series of complications among which is painful diabetic neuropathy, for which the kinin system has been implicated. Here, we review and compare the profile of several experimental models of type 1 and 2 diabetes (chemically induced versus gene-prone) and the incidence of diabetic neuropathy upon aging. We discuss the efficacy of selective antagonists of the inducible bradykinin B1 receptor (BKB1-R) subtype against hyperalgesia assessed by various nociceptive tests. In either gene-prone models of type 1 and 2 diabetes, the incidence of hyperalgesia mostly precedes the development of hyperglycemia. The administration of insulin, achieving euglycemia, does not reverse hyperalgesia. Treatment with a selective BKB1-R antagonist does not affect basal nociception in most normal control rats, whereas it induces a significant time- and dose-dependent attenuation of hyperalgesia, or even restores nociceptive responses, in experimental diabetic neuropathy models. Diabetic hyperalgesia is absent in streptozotocin-induced type 1 diabetic BKB1-R knockout mice. Thus, selective antagonism of the inducible BKB1-R subtype may constitute a novel and potential therapeutic approach for the treatment of painful diabetic neuropathy.