Characterization of the myo‐inositol transport system in Trypanosoma cruzi

Abstract

myo-Inositol is a growth factor for mammalian cells as well as for the pathogenic protozoa Trypanosoma cruzi. Most of the cell surface molecules in this organism rely on myo-inositol as the biosynthetic precursor for phosphoinositides and glycosylated phosphatidylinositols. The aim of this work was to investigate the process of myo-inositol translocation across the parasite cell membrane. myo-Inositol uptake was concentration-dependent in the concentration range 0.1±10 mm with maximal transport obtained at 8 mm. Using sodium-free buffers, where Na 1 was replaced by choline or K 1 , myo-inositol uptake was inhibited by 50%. Furosemide, an inhibitor of the ouabain-insensitive Na 1 -ATPase, inhibited the Na 1 -dependent and Na 1 -independent myo-inositol uptake by 68 and 33%, respectively. In contrast, ouabain, an (Na 11 /K 1 ) ATPase inhibitor, did not affect transport. Part of the myo-inositol uptake is mediated by active transport as it was inhibited when energy metabolism inhibitors such as carbonyl cyanide p-(trifluoromethoxy)-phenylhydrazone (34%), 2,4-dinitrophenol (50%), KCN (71%) and NaN 3 (69%) were added to the medium, or the temperature of the medium was lowered to 4 8C. The addition of glucose (5±50 mm) or mannose (10 mm) did not change the myo-inositol uptake, whereas the addition of 10 mm nonlabeled myo-inositol totally inhibited this transport, indicating that the transporter is specific for myo-inositol. Phloretin (0.3 mm) and phoridzin (5 mm), but not cytochalasin B, were efficient inhibitors of myo-inositol uptake. A portion of the accumulated myo-inositol is converted to inositol phosphates and phosphoinositides. These data show that myo-inositol transport in T. cruzi epimastigotes is mediated by at least two specific transporters Ð one Na 1 -dependent and the other Na 1 -independent.

Oleanonic acid from Lippia lupulina (Verbenaceae) shows strong in vitro antileishmanial and antitrypanosomal activity

“…Similar results were observed for sakuranetin (5) in our experiments against epimastigote forms of T. cruzi Y strain (IC 50 47.5 µg mL -1 , Table 2). Although the dihydrochalcone phloretin (4) did not show detectable trypanocidal activity in our work (IC 50 higher than 365 µM, Table 2), it has been described to influence the glucose metabolism of T. cruzi, T. brucei, and T. rangeli (Bakker et al 1999;Einicker-Lamas et al 2000;Miletti et al 2006). …”

Functional Characterization of Pneumocystis carinii Inositol Transporter 1

“…In Trypanosoma cruzi , the etiologic agent of Chagas disease or American trypanosomiasis, myo- inositol transport is facilitated by an energy-dependent, phloridzin-sensitive but cytochalasin B-insensitive system, suggesting that there are at least 2 transporters, a sodium-dependent and a sodium-independent one, that are operational in these parasites (42). Leishmania donovani , the agent of leishmaniasis, transports myo- inositol with a single transporter, L. donovani MIT (LdMIT), with a K m of 0.08 mM (43).…”

Lipid synthesis in protozoan parasites: A comparison between kinetoplastids and apicomplexans

“…Although myo -inositol can be produced de novo from glucose (see below), uptake of myo -inositol has been described in L. donovani [191], T. cruzi [192], and T. brucei [193]. Detailed characterization of the transporters, including functional expression in Xenopus oocytes, demonstrated that myo -inositol uptake in L. donovani promastigotes and T. brucei procyclic forms is mediated via H + -coupled electrogenic cotransport [150, 191, 194].…”