title: Effects of isocoumarins isolated from Paepalanthus bromelioides on mitochondria: uncoupling, and induction/inhibition of mitochondrial permeability transition.
abstract: Isolated mitochondria may undergo uncoupling, and in presence of Ca(2+) at different conditions, a mitochondrial permeability transition (MPT) linked to protein thiol oxidation, and demonstrated by CsA-sensitive mitochondrial swelling; these processes may cause cell death either by necrosis or by apoptosis. Isocoumarins isolated from the Brazilian plant Paepalanthus bromelioides (Eriocaulaceae) paepalantine (9,10-dihydroxy-5,7-dimethoxy-1H-naptho(2,3c)pyran-1-one), 8,8'-paepalantine dimer, and vioxanthin were assayed at 1-50 microM on isolated rat liver mitochondria, for respiration, MPT, protein thiol oxidation, and interaction with the mitochondrial membrane using 1,6-diphenyl-1,3,5-hexatriene (DPH). The isocoumarins did not significantly affect state 3 respiration of succinate-energized mitochondria; they did however, stimulate 4 respiration, indicating mitochondrial uncoupling. Induction of MPT and protein thiol oxidation were assessed in succinate-energized mitochondria exposed to 10 microM Ca(2+); inhibition of these processes was assessed in non-energized organelles in the presence of 300 microM t-butyl hydroperoxide plus 500 microM Ca(2+). Only paepalantine was an effective MPT/protein thiol oxidation inducer, also releasing cytochrome c from mitochondria; the protein thiol oxidation, unlike mitochondrial swelling, was neither inhibited by CsA nor dependent on the presence of Ca(2+). Vioxanthin was an effective inhibitor of MPT/protein thiol oxidation. All isocoumarins inserted deeply into the mitochondrial membrane, but only paepalantine dimer and vioxantin decreased the membrane's fluidity. A direct reaction with mitochondrial membrane protein thiols, involving an oxidation of these groups, is proposed to account for MPT induction by paepalantine, while a restriction of oxidation of these same thiol groups imposed by the decrease of membrane fluidity, is proposed to account for MPT inhibition by vioxanthin.
authors.affiliation: Departamento de Física e Química, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Brazil.
authors.forename: Anaísa F
authors.initials: AF
authors.lastname: Cálgaro-Helena
authors.forename: Karina F
authors.initials: KF
authors.lastname: Devienne
authors.forename: Tiago
authors.initials: T
authors.lastname: Rodrigues
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Dorta
authors.forename: Maria Stella G
authors.initials: MS
authors.lastname: Raddi
authors.forename: Wagner
authors.initials: W
authors.lastname: Vilegas
authors.forename: Sérgio A
authors.initials: SA
authors.lastname: Uyemura
authors.forename: Antonio C
authors.initials: AC
authors.lastname: Santos
authors.forename: Carlos
authors.initials: C
authors.lastname: Curti
mesh_terms: D000818:Animals; D001692:Biological Transport; D045304:Cytochromes c / Q000378:metabolism; D019281:Dimerization; D039262:Eriocaulaceae / Q000737:chemistry*; D049934:Isocoumarins / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology*; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000187:drug effects*; D008933:Mitochondrial Swelling / Q000187:drug effects; D015394:Molecular Structure; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D013438:Sulfhydryl Compounds / Q000378:metabolism
chemical_list: D049934:Isocoumarins; D013438:Sulfhydryl Compounds; D045304:Cytochromes c