Myeloperoxidase-generated phenothiazine cation radicals inactivate Trypanosoma cruzi dihydrolipoamide dehydrogenase.
Peroxidase/H2O2/phenothiazine systems irreversibly inhibit Trypanosoma cruzi dihydrolipoamide dehydrogenase (LADH). Inactivation of the parasite enzyme depended on (a) phenothiazine structure; (b) peroxidase nature; (c) incubation time and (d) the presence of a cation radical scavenger. With the myeloperoxidase/H2O2/system, promazine, trimeprazine, thioridazine, promethiazine, prochlorperazine, chlorpromazine and perphenazine were the most effective derivatives out of twelve phenothiazines studied. An electronegative substituent at position 2 of the phenothiazine ring such as Cl, or trifluoromethyl, propionyl and nitrile groups decreased or nullified phenothiazine activity. Myeloperoxidase/H2O2/, horseradish peroxidase/H2O2/, and myoglobin/H2O2/systems activated phenothiazines producing the corresponding cation radicals, myeloperoxidase being the most selective one with respect to phenothiazine structure. The myoglobin/H2O2/system activated phenothiazines that were scarcely active or inactivate with the MPO/H2O2/system, such as the trifluoromethyl derivatives. Production of phenothiazine cation radicals was demonstrated by optical spectroscopy. Phenothiazine cation radical stability depended on their structure as illustrated by promazine and thioridazine. Thiol compounds (GSH, N-acetyl-cysteine and penicillamine), aromatic aminoacids (L-tyrosine, L-tryptophan, and the corresponding peptides) and ascorbate scavenged phenothiazine cation radicals, thus preventing LADH inactivation. Comparison of the summarized phenothiazine effects with those of phenothiazines on T. cruzi suggest the role of cation radicals in phenothiazines chemotherapeutic actions.
Bioenergetics Research Centre, School of Medicine, University of Buenos Aires, Paraguay 2155, 1121 Buenos Aires, Argentina.
J
J
Gutiérrez-Correa
A O M
AO
Stoppani
D024322:Amino Acids, Aromatic / Q000494:pharmacology; D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D002412:Cations / Q000494:pharmacology*; D008058:Dihydrolipoamide Dehydrogenase / Q000037:antagonists & inhibitors*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000494:pharmacology; D005609:Free Radicals; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism / Q000494:pharmacology*; D010640:Phenothiazines / Q000737:chemistry*; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors*; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D014344:Trypanocidal Agents / Q000737:chemistry*; D014349:Trypanosoma cruzi / Q000187:drug effects / Q000201:enzymology*
D024322:Amino Acids, Aromatic; D002412:Cations; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D005609:Free Radicals; D010640:Phenothiazines; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; D013438:Sulfhydryl Compounds; D014344:Trypanocidal Agents; D006861:Hydrogen Peroxide; D009195:Peroxidase; D008058:Dihydrolipoamide Dehydrogenase; D001205:Ascorbic Acid