Observations on the metabolism of normal and arsenic-resistant Trypanosoma gambiense

The effect of some metabolic inhibitors on the oxygen uptake of Trypanosoma lewisi and Trypanosoma equiperdum

1. The oxygen uptake of Trypanosoma lewisi and T. equiperdum was measured with differential manometers using microflasks of 5 ml. capacity. Each flask contained 2–5 × 107 trypanosomes.

2. The oxygen uptake of trypanosomes in heparinized infected blood was compared with that of washed trypanosomes suspended in Ringer–phosphate–glucose solution with or without added serum or blood. With T. lewisi, the oxygen uptake began at a higher rate in the presence of blood or serum than with Ringer–phosphate–glucose solution. With T. equiperdum, the oxygen uptake in the presence of blood or serum began at almost the same rate as with Ringer–phosphate–glucose solution, but the rate of oxygen uptake decreased more rapidly in the absence of blood or serum than when it was present.

3. High concentrations of iodoacetic acid (e.g. 3·3 × 10−2m) caused an increase in oxygen uptake when tipped into heparinized normal rat blood. Similar concentrations caused an inhibition of oxygen uptake when 2·0 × 10−4m methylene blue was also present or when the blood had been treated with sodium nitrite to convert haemoglobin into methaemoglobin.

4. Iodoacetic acid caused little inhibition of oxygen uptake when T. lewisi was suspended in Ringer–phosphate solution containing glutamine or glutamine plus glucose, or when heparinized infected blood was tested. Inhibition was greatest when the substrate was glucose, while glucosamine, glycerol, or glucose plus serum gave intermediate results.

5. Iodoacetic acid caused least inhibition of oxygen uptake when T. equiperdum was suspended in Ringer–phosphate solution containing glycerol, or when heparinized infected blood was tested. Inhibition was greatest when the substrate was glucose, and was slightly less marked when the substrate was glucose plus serum or glucose plus glycerol.

6. Neoarsphenamine inhibited the oxygen uptake of T. lewisi to a similar extent whether glucose or glutamine was present.

7. Neoarsphenamine and reduced stovarsol thioglycollate inhibited the oxygen uptake of T. equiperdum slightly less when the substrate was glycerol than when it was glucose. Sodium arsenite was as active as reduced stovarsol thioglycollate when the substrate was glucose, but 10−4m sodium arsenite had little effect when the substrate was glycerol.

Drug resistance in trapanososmes: cross-resitance analyses

Eight strains of Trypanosoma rhodesiense, made resistant respectively to atoxyl, butarsen, acriflavine, stilbamidine, Surfen C, suramin, and pontamine sky blue 5BX, have been examined for cross-resistance to representatives of nine structurally dissimilar groups of trypanocide. On the basis of their predominant ionic form at blood pH, these groups are considered in three main classes: (a) feebly ionized (neutral aromatic arsenicals), (b) ionized as cations (melaminyl arsenicals and antimonials, acridine derivatives, diguanidines and diamidines, 6-aminoquinoline and 6-aminocinnoline derivatives, phenanthridinium derivatives, triphenylmethane dyes), and (c) ionized as anions (carboxylated aromatic arsenicals and sulphonated naphthylamine derivatives). The results are discussed in relation to those of other workers and to possible modes of trypanocidal drug action. Cross-resistance behaviour is not wholly explicable on an ionic basis; the results suggest that stereospecific structural changes associated with initial drug uptake occur in resistant trypanosomes.