Chemotherapy of African trypanosomiasis

Chemotherapeutic effects of Annona senegalensis in Trypanosoma brucei brucei

Mice infected with Trypanosoma brucei brucei 8/18 strain were treated orally and intramuscularly (im) with aqueous root extracts of Annona senegalensis, in doses of 27.8 mg kg-1 and 9.5 mg kg-1 respectively, for four consecutive days commencing 72 hours after the mice were infected. At these dosages the parasites were cleared from the circulation and no relapse was recorded over 60 days. The plant extract, however, had no effect on the trypanosomes when therapy was initiated at the late stages of infection, that is, about the sixth day when the parasitaemia level was 0.9 x 10(6); and all the animals died a day or two later. The herbal extracts also did not show any prophylactic action when given prior to infection. The root extract possesses different margins of safety in the mice depending on the route of administration. The therapeutic index for oral administration was 5.13, and that for im administration was 1.8. Chemical tests revealed that the plant extract contains alkaloids, saponins and tannins. Adverse reactions, especially to doses of 2.3-5.76 mg kg-1, were noted in animals that received the drug parenterally, but not when the drug was administered orally. However, A. senegalensis is shown to be therapeutically effective against T. b. brucei in mice, which agrees with the claims of Nigerian practitioners of Traditional Medicine that it is effective against trypanosomiasis in man.

Maternally derived immunity in young mice to infection with Trypanosoma brucei and its potentiation by Berenil chemotherapy

Young mice which were allowed to suckle, from birth, a mother infected with Trypanosoma brucei, or a mother whose infection had been cured before parturition with Berenil chemotherapy, were themselves immune to homologous trypanosome challenge. This immunity extended until approximately 25 days of age, and was transmitted in the colostrum/milk of the mother. Mice born of infected mothers, but transferred at birth to normal foster mothers, were susceptible to trypanosome infection. Drug prophylaxis in normal newborn mice was also effective for approximately 25 days, but in mice which, in addition, received colostral antibody from the mother, combined immunochemoprophylaxis protected the offspring for 40-50 days. Since the combination of protective strategies continued to resist challenge beyond the stage when, on its own, each component's efficacy had decayed, it may be of practical value as an approach to improved disease control under certain field conditions where trypanosomiasis prevails.

Bromoacetyl-L-carnitine: biochemical and antitrypanosomal actions against Trypanosoma brucei brucei

One of the causative agents of the African Trypanosamiases, Trypanosoma brucei brucei is able to use high intracellular carnitine concentrations and a high carnitine acetyl transferase (CAT) activity to stimulate ATP production. This paper reports that a carnitine analogue, bromoacetyl-L-carnitine, is an irreversible inhibitor of CAT from T.brucei, non-competitively inhibits carnitine uptake by T.brucei and has a potent in vitro effect against T.brucei motility and infectivity. An in vivo action in T.brucei infected mice is also reported. These results represent a new area of investigation in the important search for new antitrypanosomal agents.

Bleomycin-induced life prolongation of mice infected with Trypanosoma brucei brucei EATRO 110

The antitumour antibiotic bleomycin, supplied as commercial BlenoxaneR (a mixture of bleomycinic acids), at 7 or 14 mg/kg prolonged life greater than 30 days beyond death of controls without relapse or sign of trypanosomes in the peripheral blood of mice infected with Trypanosoma b. brucei EATRO 110. Control mice died in three to four days. The purified A2 and B2 bleomycin congeners were also active at this dose. Spermidine, spermine and hirudonine (1,8-diamidinospermidine) but not putrescine, co-administered with drug, annulled the curative effects of these compounds, as signalled by appearance of trypanosomes in the blood and death of the animals.

Curative effects of the antipiroplasms amicarbalide and imidocarb on Trypanosoma brucei infection in mice

The babesicides imidocarb and amicarbalide, which have structural similarities to the antitrypanosomatid diamidines, proved active against Trypanosoma brucei mouse infections: both cured infections when doses were administered daily for 3 days 24 h post-inoculation (curative dose imidocarb, 10 mg/kg; amicarbalide, 25 mg/kg). Mice were considered cured after survival 30 days longer than untreated infected controls, with no trypanosomes present in blood or cerebrospinal fluid smears. Both agents also cured when administered 48 and 72 h after challenge with T. brucei and prolonged the lives of animals 94 h after challenge. The results are discussed in respect to the potential of these carbanilides and their precursors, the antitumor phthalanilides, as lead compounds in chemotherapy of mammalian trypanosomiases.

An approach to the development of new drugs for African trypanosomiasis

The inability of the bloodstream form of Trypanosoma brucei brucei to decompose hydrogen peroxide forms the basis of our attempt to develop new pharmacological agents to kill these organisms. Approximately 1-3% of the oxygen consumed by these parasites appears in the form of hydrogen peroxide. Our previous observation that free radical initiators such as heme and hematoporphyrin D proved to be trypanocidal in vitro and in vivo, respectively, prompted this investigation into the mechanism of action of this class of compounds to enhance their therapeutic efficacy. The locus of H2O2 production within the trypanosome was examined using cell-free homogenates. Experiments described herein suggest that H2O2 is formed by the alpha-glycerol phosphate dehydrogenase in an adventitious manner, and that no enzymatic means of disposing of this potentially toxic compound are present with the organisms. Naphthoquinones were found to substantially increase the rate of both oxygen consumption and H2O2 production by trypanosomal mitochondrial preparations. Presumably, the naphthoquinones are acting as coenzyme Q analogues. The addition of sublytic concentrations of both naphthoquinones and heme leads to a synergistic lysis of the organisms in vitro. Another approach to increasing the susceptibility of T. b. brucei to free radical damage involved reduction of the intracellular concentration of glutathione. This was accomplished through the use of trypanocidal arsenicals. Melarsenoxide and heme acted synergistically in vitro, an effect which was further enhanced via addition of a naphthoquinone. Moreover, hematoporphyrin D and tryparsamide were shown to have a synergistic effect in T. b. brucei-infected mice.

The relationship between duration of infection with Trypanosoma brucei in mice and the efficacy of chemotherapy

Relapse of infection after drug treatment of trypanosome infections under conditions precluding re-infection has usually been ascribed to drug resistance on the part of the parasite or to under-dosage of the drug. With Trypanosoma brucei infection in mice we have obtained evidence of another type of relapse. In infections resulting from the inoculation of 1 × 105 trypanosomes, derived from a stabilate T. brucei TREU 667, treatment with diminazene aceturate (Berenil) at 40 mg/kg at either 3 or 7 days after infection elicited a permanent cure. If, however, treatment was delayed later than 14 days after infection, then all the mice relapsed. These relapses generally occurred between 20 and 50 days after treatment, but some mice remained aparasitaemic for up to 60 days. The relapsed infections were apparently not due to the survival of ‘drug-resistant’ trypanosomes, as infections derived from a stabilate isolated from a relapsed Berenil-treated mouse were also permanently cured with Berenil if treated 3 days after infection; however, if treatment was delayed until 21 days post-infection, all the mice relapsed. The cause of relapse was not related to the number of parasites inoculated, as infection resulting from initial inocula of 1 × 105 to 1 × 108 trypanosomes were all cured if treated at 3 days after infection, and all eventually relapsed if treatment was delayed until day 21. This type of relapse phenomenon was not confined to T. brucei TREU 667 but also occurred with 5 other stabi-lates of T. brucei after Berenil treatment. Treatment of T. brucei TREU 667 infections with Ethidium and Prothidium at dose levels of 7.5 and 10 mg/kg respectively was also followed by relapse if treatment was delayed for 3 weeks after infection. The possible causes of relapse under these conditions, and its implications in the study of the natural disease, are discussed.