Trypanosoma cruzi: inhibition of parasite growth and respiration by oxazolo(thiazolo)pyridine derivatives and its relationship to redox potential and lipophilicity.

Chagas' disease constitutes a therapeutic challenge because presently available drugs have wide toxicity to the host and are generally ineffective in the chronic stages of the disease. A series of oxazolo(thiazolo)pyridene derivatives were studied on Trypanosoma cruzi epimastigote growth and oxygen consumption and their electrochemical (redox) potentials and lipophilicity. The derivatives produced different degrees of parasite growth and respiration inhibition on CL Brener, LQ, and Tulahuen strains of T. cruzi epimastigotes. Respiratory chain inhibition appears to be a determinant of the trypanosomicidal activity of these compounds, since a significant correlation between respiration and culture growth inhibition was found. A similar correlation was found, within the different structural subfamilies, between toxic effects and the ability of the compounds to be oxidized in aqueous media. The inhibition of respiration and of parasite growth in culture increases with the lipophilicity of the substituents on the oxazolopyridine nucleus. No difference in the action of these derivatives was found among the different parasite strains. It is concluded that these compounds may have a potential usefulness in the treatment of Chagas' disease.

Trypanosoma cruzi: H2 complex and genetic background influence on the humoral immune response against epimastigotes.

Using A.SW, A.CA, B10.S and B10.M congenic mouse strains, we measured the IgG specific humoral immune responses against sonicated and live Trypanosoma cruzi epimastigotes. Genes located in the A background (A.SW and A.CA strains) mediate higher IgG responses against the parasite antigenic complexes than those located in the B background (strains B10.S and B10.M), regardless of the H2 haplotypes. Thus, non H2 genetic elements seem to be more important in determining differences in the total IgG immune response against T. cruzi. Whether a detectable H2 effect, in favor of the H2(s) haplotype, occurred in the A or B background, was contingent on the immunisation protocol used. Thus, the H2(s) haplotype mediates a higher IgG response in the A background, if immunised with live epimastigotes, and in the B background against sonicated epimastigotes. Most likely this represents a complex sequence of events, controlled by non-MHC genes, involving antigen handling and processing and depending on the physical form of antigen delivery.

Effects of 3-chloro-phenyl-1,4-dihydropyridine derivatives on Trypanosome cruzi epimastigotes.

A series of 3-chloro-phenyl-1,4-dihydropyridine derivatives produced different degrees of inhibition of parasite growth and respiration on clone Brener, LQ and Tulahuen strains of Trypanosome cruzi epimastigotes. Respiratory chain inhibition appears to be a posible determinant of the trypanosomicidal activity of this compounds. No difference in the action of these derivatives was found among the different parasite strains. For comparative purposes, the inhibitory effects of felodipine and nicardipine are also reported. A good correlation between toxic effects and the easiness of oxidation of the dihydripyridine ring was found. The presence of a fused ring on the dihydropyridine moiety significantly diminished the inhibitory effects.

Nitro aryl 1,4-dihydropyridine derivatives: effects on Trypanosoma cruzi.

A series of nitro aryl 1,4-dihydropyridine derivatives produced inhibition of both cell growth and oxygen consumption on Tulahuen and LQ strains, and clone Dm 28c of epimastigotes of Trypanosoma cruzi. Nicardipine was found to be the most potent derivative in both growth cell (I50 = 70 microM) and oxygen uptake (I50 = 26 microM in intact parasites, I50 = 325 microM in situ mitochondria). A correlation between the inhibitory effects on the growth cell and the apparent first order kinetic for the uptake of the 1,4-dihypyridine derivatives by T. cruzi epimastigotes was found. Thus, nicardipine, the most potent derivative, exhibited the highest apparent rate constant, ku, (0.043 min-1). On the other hand, no susceptibility differences by strains and clone Dm 28c to the action of these drugs were found.

Glutathione and trypanothione in several strains of Trypanosoma cruzi: effect of drugs.

Glutathione (GSH), trypanothione (T(SH)2) and glutathionyl spermidine (GSH-SP) concentrations were determined in the Tulahuén and LQ strains and the DM 28c clone of Trypanosoma cruzi. The concentrations of GSH, T(SH)2 and GSH-SP, expressed as nmol of GSH per g of parasite fresh weight, were 60.1, 397.8 and 103.9, respectively, for the Tulahuén strain. For the DM 28c clone, the values were 113.9, 677.9 and 164.1, respectively, and for the LQ strain they were 199.1, 1100.5 and 55.3, respectively. When the parasites were treated with 10 microM nifurtimox or 50 microM benznidazole for 2 h, the concentrations of all three reduced thiols decreased strongly. The total amount of T(SH)2 decreased by more than 50%. Treatment of the parasites with 5 mM buthionine sulfoximine, an inhibitor of GSH synthesis, for 6 h diminished the concentrations of the reduced thiols by between 27% and 53% with respect to the controls. Cyclohexylamine, an inhibitor of spermidine synthesis, decreased the concentrations of T(SH)2 and GSH-SP but not that of GSH. It is possible to conclude from this study that trypanothione is the most important thiol involved in the detoxication of nifurtimox and benznidazole in T. cruzi and that electrophilic reduced metabolites of both drugs are most probably conjugated with GSH, T(SH)2 and GSH-SP, thus decreasing their concentrations. GSH biosynthesis is an important drug target.