Ferdi Engels

Effects of apocynin, a drug isolated from the roots of Picrorhiza kurroa, on arachidonic acid metabolism

Apocynin is a constituent of root extracts of the medicinal herb Picrorhiza kurroa and has been shown to possess anti‐inflammatory properties. We investigated the effects of apocynin on the production of arachidonic acid‐derived inflammatory mediators by guinea pig pulmonary macrophages. Apocynin concentration‐dependently inhibited the formation of thromboxane A2, whereas the release of prostaglandins E2 and F2α was stimulated. Apocynin potently inhibited arachidonic acid‐induced aggregation of bovine platelets, possibly through inhibition of thromboxane formation. The present results suggest that apocynin might, beside its therapeutic effects in inflammatory conditions when given in a root extract of P. kurroa, also be a valuable tool in the development of new anti‐inflammatory or anti‐thrombic drugs.

Airway hyper‐responsiveness in allergic asthma in guinea‐pigs is mediated by nerve growth factor via the induction of substance P: a potential role for trkA

Background: The neurotrophin nerve growth factor (NGF) has been implicated as a mediator in allergic asthma. Direct evidence that inhibition of NGF‐induced activation of neurotrophin receptors leads to improvement of airway symptoms is lacking. We therefore studied the effects of inhibitors of NGF signal transduction on the development of airway hyper‐responsiveness (AHR) and pulmonary inflammation in a guinea‐pig model for allergic asthma.

Endotoxin-induced hyperreactivity of the guinea-pig isolated trachea coincides with decreased prostaglandin E2 production by the epithelial layer.

1 Pretreatment of guinea‐pigs with endotoxin (1 mg kg−1 b.w., i.p., 4 days before the experiments) results in respiratory airway hyperreactivity in vitro. Dose‐response curves with either arecoline or histamine on isolated tracheae from these animals display increased maximal contractions, and decreased EC50 values. 2 Tracheae denuded of epithelium respond with a similar hyperreactivity to histamine as observed in preparations from endotoxin pretreated animals. Removal of the epithelial layer of tracheae from endotoxin pretreated guinea‐pigs did not additionally affect the histamine dose‐response curve. 3 The cyclo‐oxygenase inhibitor indomethacin (10 μm) induces histamine hyperreactivity which is equal in intact and epithelium‐denuded tracheae from saline or endotoxin pretreated guinea‐pigs. Similar results are obtained with the combined lipoxygenase/cyclo‐oxygenase inhibitor nordihydroguaiaretic acid (10 μm). 4 Histamine (0.1 mm) induces an increase in prostaglandin E2 (PGE2) formation by the tracheal spiral in vitro, which is reduced by 34% by endotoxin pretreatment, and by about 60% following epithelium removal irrespective of endotoxin pretreatment. 5 Arachidonic acid (AA, 22 μm) stimulation of the guinea‐pig trachea in vitro induces a relaxation, and an increase in PGE2 production. In preparations lacking the epithelium, AA induces a contraction which coincides with a 60% reduced increase in PGE2 formation. These effects are not altered by endotoxin pretreatment. 6 It is concluded that the endotoxin‐induced respiratory airway hyperreactivity may be caused by a disturbed ability of epithelial cells to synthesize PGE2. The decreased formation of this prostaglandin is rather the consequence of a diminished liberation of AA from the phospholipid stores than a dysfunction of the cyclo‐oxygenase enzyme.

Mechanisms of allergy and asthma

Allergies are the result of an inappropriate reaction against innocuous environmental proteins. The prevalence and severity of allergic diseases has increased dramatically during the last decade in developed countries. Allergen-specific T helper (Th) cells play a pivotal role in the pathogenesis of allergic hypersensitivity reactions. These Th cells activate a complex immune reaction that triggers the release of potent mediators and enhances the recruitment of inflammatory cells, which in turn elicit an inflammatory response that leads to the clinical symptoms of allergic disease. The current therapies for allergic diseases focus primarily on control of symptoms and suppression of inflammation, without affecting the underlying cause. However, the knowledge about the pathophysiology of allergic diseases has substantially increased, offering new opportunities for therapeutic intervention. In this review, we will focus on current insights into the mechanism of allergic reactions.

9-and 13-hydroxy-linoleic acid posses chemotactic activity for bovine and human polymorphonuclear leukocytes

The presence of polymorphonuclear leukocytes (PMNs) within the airways is a characteristic feature of a variety of lung diseases. Pulmonary alveolar macrophages (PAMs) and epithelial cells release many different factors which contribute to the recruitment of inflammatory cells into infected airways. PAMs and tracheal epithelial cells are able to produce linoleic acid metabolites (9-HODE and 13-HODE) besides arachidonic acid metabolites. The objective of the present study was to determine whether 9-HODE and 13-HODE possess chemotactic activity for isolated PMNs. It was found that 9-HODE and 13-HODE induced a chemotactic response of both human and bovine PMNs in vitro. The HODEs evoked chemotaxis with a linear dose response from 10(-10) to 10(-6) M to the same extent as the arachidonic acid metabolite 15-HETE. At 10(-8) M, 9-HODE and 13-HODE were approximately half as potent in inducing chemotaxis as compared to LTB4.

The role of sensory nerve endings in nerve growth factor-induced airway hyperresponsiveness to histamine in guinea-pigs

Nerve growth factor induces an airway hyperresponsiveness in vivo in guinea‐pigs, as we have shown previously. Since antagonizing the neurokinin‐1 (NK1) receptor can prevent this NGF‐induced airway hyperresponsiveness and since sensory nerves release tachykinins, we investigated the role of sensory nerves in the NGF‐induced airway hyperresponsiveness. We used isolated tracheal rings from guinea‐pigs to measure tracheal contractility. In these rings sensory nerve endings are present, but these endings lack any contact with their cell bodies. In this in vitro system, NGF dose‐dependently induced a tracheal hyperresponsiveness to histamine. The NK1 receptor antagonist SR140333 could block the induction of tracheal hyperresponsiveness. To further investigate the involvement of sensory nerve endings we used the cannabinoid receptor 1 (CB1) agonist R‐methanandamide to inhibit excitatory events at the nerve terminal. The CB1 receptor agonist was capable of blocking the tracheal hyperresponsiveness to NGF in the isolated system, as well as the airway hyperresponsiveness to NGF in vivo. This indicates that NGF can induce an increase in airway responsiveness in the absence of sensory nerve cell bodies. NGF may act by increasing substance P release from sensory nerve endings, without upregulation of substance P in the neurons. Substance P in its turn is responsible for the induction of the NGF‐induced airway hyperresponsiveness.

Antibodies directed against nerve growth factor inhibit the acute bronchoconstriction due to allergen challenge in guinea‐pigs

We have previously demonstrated that the administration of nerve growth factor (NGF) to guinea‐pigs results in airway hyper‐responsiveness within 1 h.

TrkAd5: A Novel Therapeutic Agent for Treatment of Inflammatory Pain and Asthma

Elevated levels of nerve growth factor have been linked to the onset and persistence of many pain-related disorders and asthma. Described here are the design, expression, refolding, and purification of a monomeric (nonstrand-swapped) form of the binding domain of the nerve growth factor receptor, designated TrkAd5. We have shown that TrkAd5 produced recombinantly binds nerve growth factor with picomolar affinity. TrkAd5 has been characterized using a variety of biophysical and biochemical assays and is shown here to be stable in both plasma and urine. The palliative effects of TrkAd5 are demonstrated in animal models of inflammatory pain and allergic asthma. We conclude that TrkAd5 will prove effective in ameliorating both acute and chronic conditions where nerve growth factor acts as a mediator and suggest a role for its application in vivo as a novel therapeutic.

Cigarette smoke suppresses in vitro allergic activation of mouse mast cells.

Background Mast cells are important effector cells in innate or acquired immunity that contribute to host defence. Excessive activation of mast cells can result in the development of allergic diseases, including atopic asthma. Mast cell activation by IgE and specific antigen induces the cells to release spasmogenic, vasoactive and pro‐inflammatory mediators, which enhance airway smooth muscle contraction, vascular permeability and inflammatory cell recruitment. Recently, we have demonstrated that exposure of mast cells to cigarette smoke medium (CSM) triggered mast cells to produce chemokines. On the other hand, smoking may decrease the risk of allergic sensitization, which could be explained by a reduced IgE production or a diminished response of mast cells to activation of the IgE receptor.

Autoradiographic localization of changes in pulmonary β-adrenoceptors in an animal model of atopy

Vaccination of guinea pigs with Haemophilus influenzae leads to an impairment of beta-adrenoceptor function in lung. We have used an autoradiographic technique to study the distribution of changes in lung beta-adrenoceptor density. H. influenzae induced a decrease in beta-adrenoceptors in peripheral lung membranes of 22 +/- 5% (mean +/- S.E.M., n = 7), while the affinity of binding was unaffected. Tracheal beta-adrenoceptor binding was not influenced by H. influenzae. Autoradiography revealed a 27% reduction in beta-adrenergic binding sites on alveolar septa. Bronchial epithelial beta-adrenoceptors were decreased for 36%, and vascular smooth muscle and endothelial beta-adrenoceptors were also reduced. beta-Adrenoceptors on airway smooth muscle were unaffected. H. influenzae affected both the beta 1- and beta 2-subtypes of receptors. It is concluded that in this animal model of atopy beta-adrenoceptors may be decreased on several different cell types within the lungs, which may influence overall airway and vascular reactivity.