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

Metabolism and distribution of phenanthridine trypanocides in Trypanosoma brucei

Phenanthridine trypanocides (isometamidium chloride hydrochloride, ISM, and Ethidium bromide, EBr) have been widely used to treat African trypanosomiasis in livestock for more than 40 years. Their main action is to inhibit nucleic acid synthesis in trypanosome parasites, by intercalation between the DNA base pairs. They can also linearise selectively kinetoplast DNA minicircles; a form of mitochondrial DNA unique to this group of parasites. However, the metabolism of these compounds by trypanosomes has not been reported. Indeed, it is not known whether or not their metabolism by the parasite contributes to their activity, selective toxicity for these parasites or to the development of chemoresistance. Therefore, we studied the metabolism of EBr and ISM, and their distribution in Trypanosoma brucei (TREU 927) using high performance liquid chromatography (HPLC), liquid chromatography combined with mass spectrometry (LC-MS) and confocal laser scanning microscopy (CLSM). Incubation of EBr with trypanosomes led to the formation of a small amount (0.606+/-0.191%) of one metabolite (MI). Ion chromatograms extracted from an LC-MS analysis using electrospray ionisation (ESI), showed that the difference in mass between the parent compound and its metabolite was 30. This may correspond to the addition of a hydroxyl and a methyl group. No metabolites could be detected for ISM. The distribution of the two drugs in trypanosomes was investigated by CLSM, using their intrinsic fluorescence. ISM and EBr showed differences in their distribution in trypanosomes. ISM had a greater affinity for the kinetoplast than EBr and it stained other organelles like the flagellum; in contrast the distribution of EBr was more diffuse.

Intracellular localization and metabolism of the phenanthridinium trypanocide, ethidium bromide, by isolated rat hepatocytes

1. Confocal laser scanning microscopy (CLSM) has shown that ethidium (3 ,8-diamino-5-ethyl-6-phenylphenanthridinium) bromide, an aromatic phenanthridinium trypanocide, is taken up rapidly into the nucleoli and nuclear membranes of isolated rat hepatocytes. 2. It is biotransformed by the hepatocytes and at least five metabolites have been detected by high-performance liquid chromatography (HPLC). 3. Two new metabolites, 3- and 8-N-glucuronosylethidium, have been identified by HPLC-electrospray mass spectrometry and they represent the major pathway of metabolism, accounting for 6.4 +/- 0.7 and 19.5 +/- 1.2% respectively of total recovered drug after incubation. A third metabolite, 3,8-diacetylethidium, is formed in trace quantities. 4. The other two metabolites, 3-acetylethidium and 8-acetylethidium, have been reported previously.

Redox cycling of o-naphthoquinones in trypanosomatids. Superoxide and hydrogen peroxide production

beta-Lapachone and structurally related lipophilic o-naphthoquinones, namely, CG 8-935, CG 9-442, CG 10-248 and mansonones A, C, E, and F, were investigated for redox cycling, production of reactive oxygen species, and cytotoxicity in the trypanosomatids Crithidia fasciculata and Leptomonas seymouri. Structural analysis of the assayed quinones indicated that a tricyclic structure, including a naphthalene ring, a 1,2b or 1,8bc pyran ring, and two ortho-carbonyl groups were required for quinone activities. The contribution of oxygen radical production to quinone cytotoxicity was supported by: (a) spectroscopic observation of quinone redox cycling; (b) production of the semiquinone radical; (c) H2O2 and O2- production; (d) the effect of beta-lapachone on thiol pools in C. fasciculata; (e) the effect of quinones on cell respiration; (f) superoxide dismutase inactivation after incubation of C. fasciculata with CG 8-935; and (g) the effect of quinones on cell growth.

Bioavailability, pharmacokinetics, and tissue distribution of 14C homidium after parenteral administration to Boran cattle

The absorption, distribution and elimination characteristics of 14C homidium have been described in non-infected and Trypanosoma congolense-infected cattle treated with 14C homidium chloride by either intramuscular (i.m.) or intravenous (i.v.) injection at a dose level of 1 mg/kg body weight. Results show that the mean (+/-SD) elimination of the drug from plasma followed a biexponential process, with half-lives of 0.084 +/- 0.006 h and 97.66 +/- 16.28 h for the distribution and elimination phases after intravenous injection, respectively. Bioavailability of the intramuscular dose was 62.5% and 57.8% in non-infected and trypanosome-infected cattle, respectively. Absorption was rapid, with a tmax of 15 min and a mean Cmax (+/-SD) of 268.4 +/- 4.09 ng/mL following the intramuscular dose in non-infected cattle. The major route of excretion was via faeces. Approximately 90% of the total dose given to non-infected i.m.-treated cattle was excreted within 14 days. Following intramuscular administration of the drug, residues remained high in the major excretory organs, with the liver having concentrations of 1411 and 1199 ng/g after 14 and 28 days, respectively. Over the same period, the values in the kidneys were 649 and 448 ng/g. Concentrations in the liver 14 and 21 days following i.v. treatment were 2195 and 2454 ng/g, respectively. These results show that there was no significant difference in liver drug residues between 14 and 21 days, or 28 days depending on the treatment given, suggesting that once the drug is in this organ, it is released back into the circulation at an extremely slow rate.

Flow cytofluorimetric analysis of drug accumulation by multidrug-resistant Trypanosoma brucei brucei and T. b. rhodesiense

Dual laser flow cytofluorimetry has been used to compare accumulation of compounds representing three major classes of trypanocidal drugs by drug sensitive and drug resistant clones of Trypanosoma brucei brucei and T. b. rhodesiense. Clones selected for resistance to melarsoprol were shown to be cross-resistant in vivo to two diamidines, pentamidine and Berenil, but not to suramin. At 35 degrees C, bloodstream forms of these multidrug-resistant clones accumulated lower intracellular concentrations of the diamidines 4',6-diamidino-2-phenyl-indole (DAPI) and Hoechst 33342, the phenanthridine ethidium bromide, and the acridine acriflavine than drug sensitive parasites. Accumulation of all four drugs was saturable. Drug concentrations giving half-maximal rates of accumulation were increased in the resistant clones relative to the sensitive parent clones. The rate of DAPI accumulation by both resistant and sensitive parasites was strongly temperature dependent and increased sharply above 27 degrees C. Two distinct populations were resolved in mixtures of sensitive and resistant clones exposed to DAPI. Resistant and sensitive cells accumulated identical intracellular concentrations of DAPI following brief treatment with the detergent Triton X-100. The results suggest that alterations in the surface membrane of multidrug-resistant trypanosomes reduce accumulation of several drugs relative to drug sensitive parasites.