title: The Characterization of an Adrenergic Signalling System Involved in the Encystment of the Ocular Pathogen Acanthamoeba spp.
abstract: The aim of this study was to identify and characterize the receptor system involved in controlling encystment in Acanthamoeba using specific agonists and antagonists and to examine whether endogenous stores of catecholamines are produced by the organism. Acanthamoeba trophozoites suspended in axenic growth medium were exposed to adrenoceptor agonists and antagonists to determine which compounds promoted or prevented encystment. Second, trophozoites were cultured in medium containing a catecholamine synthesis inhibitor to investigate the effect this had on natural encystment. Nonspecific adrenoceptor agonists including epinephrine, isoprotenerol, and the selective β1 adrenoceptor agonist dobutamine were found to cause > 90% encystment of Acanthamoeba trophozoites compared to < 30% with the controls. The selective β1 antagonist metoprolol was able to inhibit epinephrine mediated encystment by > 55%. Cultures of Acanthamoeba with the catecholamine synthesis inhibitor α-methyl-p-tyrosine significantly reduced the level of amoebic encystment compared to controls. In conclusion, Acanthamoeba appear to contain a functional adrenergic receptor system of unknown structure which is involved in initiating the encystment process that can be activated and blocked by β1 agonists and antagonists respectively. Furthermore, the presence of this receptor system in Acanthamoeba indicates that topical β adrenoceptor blockers may be effective adjunct therapy by reducing the transformation of trophozoites into the highly resistant cyst stage.
authors.affiliation: School of Biomedical Science, University of Wolverhampton, MA Building, Wulfruna Street, Wolverhampton, WV1 1LY, United Kingdom.
authors.forename: Wayne
authors.initials: W
authors.lastname: Heaselgrave
authors.affiliation: Department of Infection Immunity and Inflammation, University of Leicester, Medical Sciences Building, University Road, Leicester, LE1 9HN, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Kilvington
mesh_terms: D000048:Acanthamoeba / Q000187:drug effects* / Q000254:growth & development / Q000472:pathogenicity*; D018663:Adrenergic Agents / Q000494:pharmacology*; D000322:Adrenergic Agonists / Q000494:pharmacology; D000818:Animals; D002395:Catecholamines / Q000096:biosynthesis; D003470:Culture Media; D046508:Culture Techniques; D004837:Epinephrine / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D000069289:Parasite Encystment / Q000187:drug effects*; D011941:Receptors, Adrenergic / Q000187:drug effects; D053058:Trophozoites / Q000187:drug effects / Q000254:growth & development
chemical_list: D018663:Adrenergic Agents; D000322:Adrenergic Agonists; D002395:Catecholamines; D003470:Culture Media; D011941:Receptors, Adrenergic; D007545:Isoproterenol; D004837:Epinephrine
keywords: Adrenoceptor; catecholamine; cyst; epinephrine; trophozoite