Differences in the effects of a putrescine analogue on polyamine biosynthesis and transport in Giardia and Leishmania spp

MAIA C; VALENTIM C; CARRILLO C; ALGRANATI ID; MELLO FG; VANNIER DOS-SANTOS MA

Caxambú, Brazil

Congreso; XXIX Reunião Anual de Pesquisa em Doença de Chagas e XVIII Reunião Anual de Protozoologia; 2002

Giardiasis and leishmaniasis are wordwide re-emerging diseases, which affect undeveloped and developed countries. As other cell types, these parasitic protozoa synthesize polyamines (PAs) which are organic polycations involved in the regulation of metabolic processes such as cell division and differentiation. PAs are also potent antioxidant molecules protecting nucleic acids and membranes from peroxidation. In most cells PA synthesis is initiated by decarboxylation of ornithine to putrescine by ornithine decarboxylase (ODC). Nevertheless, Giardia does not rely solely on ornithine but instead on agmatine as the putrescine precursor. We have shown that the putrescine analogue 1,4-diamino-2-butanone (DAB) impairs Leishmania and G. lamblia division. Nevertheless, the mechanism of action of this compound seems different for both parasites. In the aerobic Leishmania DAB targets the single mitochondrion leading to complete destruction of the organelle (Valentim et al., submitted). Instead, the amitochondriate Giardia trophozoites evolved to a cyst-like form (Maia et al., submitted), suggesting that PAs may have distinct roles in divergent parasites. In this study we have focused the effects of DAB treatment on ODC activity and PA transport. The ODC activity of trophozoites is extremely low (99 pmol CO2/h/mg protein) as compared to other cell types and was not significantly affected by either pretreatment (89,91 pmol CO2/h/mg protein) or addition of DAB during the assay (119.63 pmol CO2/h/mg protein). The putrescine transport was also assayed in the presence of DAB. Both Leishmania developmental forms (promastigotes and amastigotes) take up [3H]-putrescine. Addition of 100µM DAB during the assay (90 min) resulted in a 3-fold inhibition of  [3H]-putrescine incorporation by amastigotes (0.114 vs. 0.035 pmol [3H]-putrescine/108 cells) while a 24h-pretreatment, followed by the removal of the drug during uptake measurement, increased the uptake by 2-fold (0.231 pmol [3H]-putrescine/108 cells). As for amastigotes, DAB pre-treatment also increased by 1.5-fold the putrescine uptake by promastigotes (111 vs. 173 pmol [3H]-putrescine/108 cells). Giardia did not incorporate this PA and, as expected, the uptake was not affected by DAB. The data suggests that this compound enters this cell by a non-specific PA transporter and corroborates the distinct mechanisms by which DAB acts in these parasites.   Supported by: PROCAD/CAPES, FAPERJ, CNPq.