Nursing Pharmacology Chapter 25:  Pulmonary Pharmacology: Asthma

 

¹Mechanisms involved in pathology associated with asthma

• A generalized tracheobronchial hyperirritability is a central aspect of asthma. 

  • Airway reactivity may vary and with heightened reactivity more obvious and severe symptoms present and more aggressive pharmacotherapy are required. Lung function exhibits fluctuations throughout the day with dyspnea more apparent at night and in the early morning. 

  • Airway reactivity varies in all individuals as a function of exposure to oxidant air pollutants as well as following respiratory tract viral infections.

  • Of these two insults, viral infections are more predominant in their long-term effects on airway reactivity.

  • Furthermore, allergens produce rapid increases in airway responsiveness (reactivity) which remains heightened for weeks. With significant allergen exposure, obstruction may occur rapidly and last for some time. 

• The current working framework for the understanding of asthma is based on the presence of continual airway inflammation which can be exacerbated under certain circumstances. 

  • Asymptomatic asthmatic patients therefore exhibit the presence of inflammation confirmed by endobronchial biopsy.

    • The airway is characterized as edematous with eosinophil, neutrophils, and lymphocyte infiltration.

    • Increased capillary density with increased cellularity represents probably the most common finding.

  • Overall asthma manifestation is probably a complex result of interactions between airway inflammatory cells, inflammatory mediators, cytokines, and surface epithelium.

  • Cell types most likely involved include mast cells, eosinophils, epithelial cells, and lymphocytes.

    • Also, there is the possibility of macrophage and neutrophil involvement.

    • Cells primarily involved release mediators which include: histamine, leukotrienes (C, D & E), bradykinin, platelet-activating factor, and prostaglandins (E₂, F₂, & D₂).

• The above mediators produce an immediate, intense inflammation that is characterized by vascular congestion, edema, and bronchoconstriction. 

  • Leukotrienes which act to promote airway smooth muscle contraction as well as mucosal edema also may inhibit mucociliary transport and increase mucus production. 

• Chronic events follow these initial actions with chemotactic factors recruiting eosinophils, polymorphonuclear leukocytes, and platelets to the reaction site.

  • "Chemokines: (chemoattractant cytokines) are short soluble peptides (70-90 amino acids) which can be divided into two groups.

    • Alpha (or C-X-C) chemokines contain a single amino acid between the first and second cysteine residues, and are primarily involved in neutrophil activation.

    • Beta (or C-C) chemokines have adjacent cysteine residues and are generally involved in activation of monocytes, lymphocytes, basophils and eosinophils"⁶.

    • These chemotactic factors include eosinophil and neutrophil anaphylactic factors and leukotriene B₄.

      • These recruited cells in addition to macrophages already present as well as the bronchial epithelium provides sources for additional mediators enhancing immediate and cellular phases. 

  • Airway epithelial cells serve both as a target and a contributor to the inflammation process since they amplifying the bronchoconstrictive aspect by liberating endothelin-1 and enhance vasodilatation by liberation of nitric oxide ( ), PGE₂ as well as the 15-hydroxyeicosatetranoid acid (15-HETE) arachidonic acid metabolic products. These cells also produce cytokines including:

    • Granulocyte-macrophage colony stimulating factor (GM-CSF)

    • Interleukin (IL)8

    • Rantes

    • Eotaxin

      • Eotaxin is an eosinophilic chemoattractant cytokine which is upregulated in allergic airways inflammation. Figure below:  attribution--Tim Williams PhD, Imperial College of Medicine, South Kensington, London.

      • ⁸The accumulation of eosinophilic leukocytes in the lungs of asthmatic patients is probably due to the effect of chemoattractant small molecules. Eotaxin has been identified as a potent eosinophil chemoattractants that is produced by several different cells in the stimulated by interleukin-4 and interleukin-13, both of which are synthesized by T-helper (Th2) lymphocytes. 

      • ⁸Eotaxin interacts with the eotaxin receptor which is a C-C chemokine receptor (CCR)₃. Small molecules have been synthesized without interfere with eotaxin binding to its chemokine receptor, suggesting a possible therapeutic intervention that will limit eosinophilic recruitment in the lung with subsequent possible prevention of damage and pulmonary dysfunction.

      • ⁸The eosinophil represents a white cell that has a two-lobed (bilobed) nucleus and has cytoplasmic granules which stain pink following exposure to eosin. 

        • It has been suggested that eosinophils are important in the immunological defense system against helminths (worms). 

        • Parasitic worms causing immunological response particularly towards TH2 lymphocytes which regulate IgE production. Immunoglobulin E binds to mast cells providing the means for specific antigen recognition (especially important in acute responses to worms). 

        • TH2 lymphocytes regulate eosinophil accumulation important chronic responses to worms. 

        • In eosinophils accumulating around these parasites then become stimulated to release O (free radicals) molecules as well as toxic proteins.

        • According to this view, allergy may be a host response originally developed against helminths but now triggered in an inappropriate manner by other stimuli. 

        • The particular importance of eotaxin is that it provides the mechanisms by which selective eosinophil accumulation may be mediated, given that other chemoattractants have more generalized effects (i.e. they promote neutrophil attraction.)

      • ⁸Concerning the eotaxin receptor: there been > 50 chemokines identified. 

        • Most chemokines produce effects by mediation through several different receptors; however, eotaxins are fairly unusual in that there signaling process involves a single receptor, the CCR₃ receptor.

        • The CCR₃ receptor has been found also on TH2 lymphocytes which regulate eosinophilic recruitment. 

• ¹ Whereas the mast cell is important in the early stages of the reaction, eosinophils play a central role in the infiltrative aspect. 

  • Granular eosinophilic proteins (eosinophilic cationic protein & basic protein) as well as oxygen-derived free radicals probably destroyed the airway epithelial lining medicine and sloughed into the bronchial lumen as ⁵Creola bodies.

    • 5Attribution for the Creola body image:  S U N Y Upstate Medical University, Content maintained by: Susan Stowell, copyright © 2002, SUNY Upstate Medical University; 5"Creola bodies ...are characterized... by cilia, the evenly distributed chromatin, and the smooth nuclear membranes"

       

  • ¹ Damage described above not only affects barrier and secretory processes but also causes additional chemotactic cytokine production which promotes additional inflammatory responses.

    • T lymphocytes are central to the inflammatory response with an increased presence in the asthmatic airway; furthermore,T lymphocytes are activators of cell-mediated immunity through cytokines as well as humoral (IGE) immune reactions.

    ¹ Cytokine production:

    • This process is an important, vital component in asthma inflammatory processes. Cytokines synthesized and released from these inflammatory cells discussed earlier as well as from epithelial cells, fibroblasts, endothelial cells, and airway smooth muscle activate many specific cell-surface receptors.

    • Cytokines that are thought to most important in asthma pathogenesis and are secreted by T lymphocytes are: 

      1. IL-3 -- lengthens mast cell survival

      2. IL-4 & IL-13 -- activates B lymphocytes IgE synthesis and adhesion molecule expression. 

      3. IL-5 -- differentiation and lengthens eosinophil survival.

    • Pro- inflammatory cytokines which also could amplify the inflammatory response include IL-1B, IL-6, IL-11, tumor necrosis factor (TNF-) and GM-CSF .

 

• ¹ McFadden, E.R., Jr. "Asthma: Diseases of the Respiratory System" in Harrison's Principles of Internal Medicine, 15th Edition (Braunwald, E., Fauci, A.S., Kasper, D.L., Hauser, S.L, Longo, D.L. and Jameson, J.  Larry, eds) pp. 1456-1463,  McGraw-Hill Medical Pubishing, Division, New York, 2001

• ² Kelley, H. William, "Asthma" in  Pharmacotherapy:  A Pathophysiologic Approach, (Dipiro, J.T., Talkbert, R.L.  Yee, G.C., Matze, G.R., Wells, B.G. and Posey, L. Michael, eds.)  pp 430-459. McGraw-Hill Medical Pubishing, Division, New York, 1999.

• ³Spencer SM., Sgro JY., Dryden KA., Baker TS., Nibert ML. (1997) Rhinovirus 14 (3D image reconstruction from electron microscopy data) Journal of Structural Biology. 120(1):11-21

• ⁴Attribution:  Michigan State University Website:

• ⁵State University of New York, Upstate Medical University, Cytotechnology, On-Line Courseware,

• ⁶Steve Dewhurst, Ph.D., Structure of the CC-chemokine, RANTES, (c) University of Rochester and Stephen Dewhurst, 1999

• ⁷Ealick SE, Recombinant Human Granulocyte-Macrophage Colony-Stimulating Factor, Cornell University

  • Walter MR, Cook WJ, Ealick SE, Nagabhushan, TL, Trotta, PP and Bugg, CE. Three-Dimensional Structure of Recombinant Human Granulocyte-Macrophage Colony-Stimulating Factor, J. Mol. Biol. 224:1075-1085 (1992).

  • Reichert P, Ealick SE, Cook WJ, Trotta P, Nagabhushan TL, Bugg CE. Crystallization and Preliminary X-ray Investigation of Human Granulocyte-Macrophage Colony Stimulating Factor, J. Biol. Chem. 265(1):452-453 (1990)

• ⁸Williams, TJ and Conroy, TM  Eotaxin and the attraction of eosinophils to the asthmatic lung, Respir Res 2001, 2: 150-156

• ⁹McFadden, Jr., E. R., Diseases of the Respiratory System: Asthma, In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, p 1422.

• ¹⁰Daroca, P, Lung and Respiratory System Review, Tulane University Pathology, (Figure & caption attribution)