Date Published: December 16, 2008
Publisher: Public Library of Science
Author(s): Fernanda Fraga Campos, Luiz Henrique Rosa, Betania Barros Cota, Rachel Basques Caligiorne, Ana Lúcia Teles Rabello, Tânia Maria Almeida Alves, Carlos Augusto Rosa, Carlos Leomar Zani, Serap Aksoy
Abstract: Protozoan parasites belonging to genera Leishmania and Trypanosoma are the etiological agents of severe neglected tropical diseases (NTDs) that cause enormous social and economic impact in many countries of tropical and sub-tropical areas of the world. In our screening program for new drug leads from natural sources, we found that the crude extract of the endophytic fungus Cochliobolus sp. (UFMGCB-555) could kill 90% of the amastigote-like forms of Leishmania amazonensis and inhibit by 100% Ellman’s reagent reduction in the trypanothione reductase (TryR) assay, when tested at 20 µg mL−1. UFMGCB-555 was isolated from the plant Piptadenia adiantoides J.F. Macbr (Fabaceae) and identified based on the sequence of the internally transcribed spacer (ITS) regions of its ribosomal DNA. The chromatographic fractionation of the extract was guided by the TryR assay and resulted in the isolation of cochlioquinone A and isocochlioquinone A. Both compounds were active in the assay with L. amazonensis, disclosing EC50 values (effective concentrations required to kill 50% of the parasite) of 1.7 µM (95% confidence interval = 1.6 to 1.9 µM) and 4.1 µM (95% confidence interval = 3.6 to 4.7 µM), respectively. These compounds were not active against three human cancer cell lines (MCF-7, TK-10, and UACC-62), indicating some degree of selectivity towards the parasites. These results suggest that cochlioquinones are attractive lead compounds that deserve further investigation aiming at developing new drugs to treat leishmaniasis. The findings also reinforce the role of endophytic fungi as an important source of compounds with potential to enter the pipeline for drug development against NTDs.
Partial Text: Protozoan parasites belonging to the genera Leishmania and Trypanosoma (order Kinetoplastida, family Trypanosomatidae) occurs in the tropical and sub-tropical areas of the world, where they cause severe diseases with huge medical, social, and economic impact to millions of people . All diseases caused by these parasites are among the Neglected Tropical Diseases (NTDs) listed by the World Health Organization . Different species of Leishmania affects over 12 million people and puts over 350 million people at risk in 88 countries; Trypanosoma cruzi infects approximately 8 million and puts 100 million at risk in Central and South America, and T. brucei infects 60 million people in 36 sub-Saharan African countries . The drugs currently available to treat the different forms of leishmaniasis and trypanosomiasis were introduced many decades ago and have significant drawbacks, especially in terms of efficacy, length of treatment, route of administration, toxicity, and cost . To complicate the situation, there is no new drug being developed by the major pharmaceutical industries for these diseases .
Several endophytic fungi were isolated from the P. adiantoides, a plant species selected due to the activity of its extract in a panel of assays used to screen the Brazilian flora for bioactive natural products (unpublished results). Among the fungi isolated from this plant, the isolate UFMGCB-555 showed strong activity in the assays with TryR and L. amazonensis. Using molecular taxonomy techniques, we were able to identify this fungus as Cochliobolus sp. (Pleosporaceae, Ascomycota). This genus comprises approximately 50 species occurring all over the world , many of which can parasitize plants and cause considerable agricultural losses . Some species of Bipolaris, the anamorphic state of Cochliobolus, are also the etiologic agent of several human diseases, such as sinusitis, ocular infections, peritonitis, and meningoencephalitis ,. However, in the present work we looked for the ability of Cochliobolus UFMGCB-555 to produce secondary metabolites with biological or pharmaceutical potential, especially for neglected tropical diseases.