Inhibition by several standard antiprotozoal drugs of growth and O2 uptake of cells and particulate preparations of a Leptomonas

Implications of co-infection of Leptomonas in visceral leishmaniasis in India

Protozoan parasites Leishmania donovani (family: Trypanosomatidae) cause fatal visceral leishmaniasis (VL) and the infection relapses in apparently cured population as post kala-azar dermal leishmaniasis (PKDL) in the Indian subcontinent. In recent years co-infection of another Trypanosomatid parasite Leptomonas with L. donovani during VL/PKDL in this region has become prominent. The observation of clinically lesser-known insect parasite, Leptomonas in leishmaniasis is intriguing to researchers. The presence of Leishmania look alike Leptomonas in the cultures of clinical isolates of Leishmania has been worrisome to those, who prefer to work with pure Leishmania cultures for drug and vaccine development or immune response studies. The exact implications of such a co-habitation, which might lead to a delay in the diagnostics of VL and elevate mortality, need a thorough investigation. Also whether Leptomonas is involved in leishmaniasis manifestation needs to be ascertained. Thus we are currently witnessing a new paradigm of a parasitic co-infection in VL/PKDL cases in India and this review outlines various opportunities for further research in understanding such emerging co-infection.

Characteristics of ethidium uptake by the trypanosomatid flagellates Crithidia fasciculata and Leptomonas seymouri

The uptake of the phenanthridinium ethidium by the trypanosomatids Crithidia fasciculata and Leptomonas seymouri was studied. The time course of uptake of ethidium was biphasic for both organisms, consisting of an initial rapid phase and a protracted slow phase. The characteristics of these phases were consistent with the hypothesis that the initial phase represented specific external binding, while the second phase represented transport into the cells. In L. seymouri the transport phase was inhibited by inhibitors of energy transduction and putative inhibitors of a transport ATPase. Ethidium transport could not be saturated over a large concentration range of ethidium. Phenanthridiniums and related compounds displayed both inhibitory and stimulatory effects on ethidium transport.

Uptake of the trypanocidal drug suramin by bloodstream forms of Trypanosoma brucei and its effect on respiration and growth rate in vivo

After a single intravenous injection of suramin the rate of removal of the drug from the plasma into other tissue compartments of the rat is independent of initial concentration. The data can be fitted to the sum of two exponential functions, consistent with a two-compartment, open model system. Trypanosomes take up only small amounts of suramin in vivo and do not actively concentrate the drug within the cell. Uptake is apparently by a non-saturable process that decreases with time and is dependent on the amount of suramin already taken up. Once within the cell, suramin progressively inhibits respiration and glycolysis, such that, for a given exposure in vivo, inhibition of oxygen consumption is proportional to the total amount of suramin absorbed. It can be calculated that only a fraction (4--9%) of this total is required to inhibit respiration to the extent found in broken cell preparations. The combined inhibition of two key enzymes in glycolysis--the sn-glycerol-3-phosphate oxidase (EC unassigned) and the glycerol-3-phosphate dehydrogenase (NAD+) (sn-glycerol-3-phosphate: NAD+ 2-oxidoreductase, EC 1.1.1.8)--are sufficient to account for the differential inhibition of glucose and oxygen consumption and of pyruvate production, together with the small, but significant, production of glycerol. Even at the highest dose of suramin tolerated by the rat, trypanosomes continue to increase exponentially in the bloodstream for at least 6 h. The mean doubling time is increased from 4.6 h to a maximum of about 12.5 h in rats treated with doses of suramin in the range 25--150 mg/kg. In the light of these and other findings, it is concluded that part of the trypanocidal action of suramin results from the inhibition of ATP production by glycolysis.

Polyamines in trypanosomatids

Polyamines were determined by n-butanol extraction and thin-layer chromatography in four trypanosomatids: Trypanosoma brucei (rat infection) and cultures of Crithidia fasciculata, Leptomonas sp., and Trypanosoma mega. All had putrescine and spermidine but no detectable spermine. Putrescine and spermidine levels were quantitated for extracts of leptomonas during the normal growth cycle. Spermidine values peaked 18 h before peak cell populations. Spermidine-putrescine ratios for all organisms were related to the presumed phylogeny of the group.

Susceptibility of an insect Leptomonas and Crithidia fasciculata to several established antitrypanosomatid agents

Growth inhibition of the lower trypanosomatids Crithidia fasciculata and a Leptomonas from a hemipteron by several established trypanocides and leishmanicides were compared in four complex and one defined media. The Leptomonas was more susceptible than C. fasciculata in all media, especially to phenanthridines (ethidium, prothidium, isometamidium) and diamidines (pentamidine, diminazene diaceturate [Berenil], hydroxystilbamidine, stilbamidine); concentrations of these drugs required for 50% inhibition of the Leptomonas were <5 mug/ml. In contrast, C. fasciculata was uninhibited by <20 mug of diamidines per ml and was three- to sixfold less susceptible than the Leptomonas to isometamidium and prothidium. Both trypanosomatids were susceptible to nucleoside antibiotics, e.g., nucleocidin. Neither was inhibited by suramin, melarsen, melarsen oxide, or tryparsamide. The Leptomonas was more susceptible to standard trypanocides than five other insect trypanosomatids in a complex medium; it was the only one inhibited by <20 mug of stilbamidine and hydroxystilbamidine per ml.