Activation of leukotriene synthesis in human neutrophils by exogenous arachidonic acid: inhibition by adenosine A(2a) receptor agonists and crucial role of autocrine activation by leukotriene B(4).
We report here that the apparent inability of isolated human polymorphonuclear leukocytes (PMNs) to efficiently transform arachidonic acid (AA) is the consequence of A(2a) receptor engagement by endogenous adenosine accumulating in incubation media. Indeed, when adenosine is eliminated from PMN suspensions by the addition of adenosine deaminase, or when cells are incubated with adenosine A(2a) receptor antagonists, important quantities (40-80 pmol/10(6) cells) of 5-lipoxygenase products are synthesized by PMN incubated with 1 to 5 microM exogenous AA. The selective A(2a) receptor agonist CGS21680 was a very potent inhibitor of the AA-induced leukotriene (LT) synthesis, showing an IC(50) of approximately 1 nM. The mechanism of AA-induced stimulation of LT synthesis observed in the absence of extracellular adenosine was investigated. In adenosine deaminase-treated PMN, exogenous AA induced Ca(2+) mobilization and the translocation of 5-lipoxygenase to nuclear structures. A time lag of 20 to 60 s (variable between PMN preparations) was observed consistently between the addition of AA and the elevation of intracellular Ca(2+) concentration (and LT synthesis), indicating that AA itself did not trigger the Ca(2+) mobilization in PMN. This AA-induced Ca(2+) mobilization, as well as the corresponding 5-lipoxygenase translocation and stimulation of LT synthesis, was blocked efficiently by the LT synthesis inhibitor MK0591, the LTB(4) receptor antagonists CP105696 and LY223982, and the LTA(4) hydrolase inhibitor SC57461A. These data demonstrate that AA is a highly potent and effective activator of LT synthesis and acts through a mechanism that requires an autocrine stimulatory loop by LTB(4).
Surette
M E
ME
Centre de Recherche en Rhumatologie et Immunologie, Centre de Recherche du Centre Hospitalier Universitaire de Québec, Pavillon CHUL and Faculté de Médecine, Université Laval, Quebec, Canada.
Krump
E
E
Picard
S
S
Borgeat
P
P
D000241:Adenosine / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D000322:Adrenergic Agonists / Q000378:metabolism; D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism; D016718:Arachidonic Acid / Q000378:metabolism / Q000494:pharmacology*; D019898:Autocrine Communication / Q000502:physiology; D001578:Benzopyrans / Q000494:pharmacology; D001692:Biological Transport; D001711:Biotransformation; D002118:Calcium / Q000378:metabolism; D002264:Carboxylic Acids / Q000494:pharmacology; D002467:Cell Nucleus / Q000378:metabolism; D015118:Eicosapentaenoic Acid / Q000494:pharmacology; D004851:Epoxide Hydrolases / Q000037:antagonists & inhibitors; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007700:Kinetics; D020024:Leukotriene Antagonists / Q000494:pharmacology; D007975:Leukotriene B4 / Q000494:pharmacology*; D015289:Leukotrienes / Q000096:biosynthesis*; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology; D018375:Neutrophil Activation; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism; D010627:Phenethylamines / Q000494:pharmacology; D058906:Purinergic P1 Receptor Agonists; D011804:Quinolines / Q000494:pharmacology; D043705:Receptor, Adenosine A2A; D018102:Receptors, Leukotriene B4 / Q000037:antagonists & inhibitors
D000322:Adrenergic Agonists; D001578:Benzopyrans; D002264:Carboxylic Acids; D007211:Indoles; D020024:Leukotriene Antagonists; D015289:Leukotrienes; D016859:Lipoxygenase Inhibitors; D010627:Phenethylamines; D058906:Purinergic P1 Receptor Agonists; D011804:Quinolines; D043705:Receptor, Adenosine A2A; D018102:Receptors, Leukotriene B4; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; C078266:MK 0591; D007975:Leukotriene B4; D016718:Arachidonic Acid; D015118:Eicosapentaenoic Acid; D001094:Arachidonate 5-Lipoxygenase; D004851:Epoxide Hydrolases; D000241:Adenosine; D002118:Calcium; C043134:leukotriene A4 hydrolase; C089698:CP 105696