Virginia B. Waits

Improved therapy of experimental leishmaniasis by use of a liposome-encapsulated antimonial drug

Abstract The anti-leishmanial antimonial drug meglumine antimoniate (Glucantime ®) was incorporated into liposomes, and was tested for effects against experimental leishmanial infection in hamsters. When the hamsters had been infected for a short period before treatment (3 days), treatment doses of 416 mg/kg of free meglumine antimoniate, or 4 mg/kg of liposome-encapsulated drug, each gave 99.8% suppression of parasites. After 10 or 17 days of infection prior to treatment liposome-encapsulated compound was more than 300 times as effective as the antimonial drug alone. Use of liposomes containing appropriate drugs is proposed as a markedly superior means to treat certain chronic intracellular parasitic infections.

Liposomes in leishmaniasis: effects of parasite virulence on treatment of experimental leishmaniasis in hamsters

During studies on the use of liposomes as drug carriers in experimental leishmaniasis in hamsters, we noted incidentally that the apparent virulence of the infection often varied widely between different large groups of animals. When the death rates among control animals (injected only with saline) were compared with hepatic parasite counts of survivors in the same group, three distinctive types of infection were observed: type I, low death rate, low parasite count in survivors; type II, high death rate, low parasite count in survivors; type III, high death rate, high parasite count in survivors. The apparent virulence, based on death rates both at early and late stages of infection, was in the order I less than II less than III. Therapeutic efficacy of a drug (meglumine antimoniate) or liposome-encapsulated drug against each type of infection was in the order I greater than II greater than III. Liposomes reduced the drug dose required for each infection type many hundred-fold and reduced the death rate for type I to zero. However, among animals with type III (or even type II) infection certain individuals were completely refractory to treatment, even when liposome-encapsulated drug was employed, and the lowest mortality rate achieved was approximately 30%. This latter resistance to treatment may have been due to irreversible tissue damage caused by advanced disease, or it may have reflected resistance of certain virulent infections to treatment.

Immunization of mice with irradiated Trypanosoma cruzi grown in cell culture: Relation of numbers of parasites, immunizing injections, and route of immunization to resistance

Abstract Mice were given 5 or 8 weekly injectins of either 2·0 × 10 6 or 20·0 × 10 6 irradiated T. cruzi from cell culture (ratio of trypomastigotes to amastigotes, 1 : 1) via the intraperitoneal route or via the subcutaneous route and challenged via the subcutaneous route one week after the last injection with 5·0 × 10 4 T. cruzi in mouse blood. The irradiated parasites used were not capable of producing infections in either Vero cell cultures or C 3 H mice. Mice receiving irradiated parasites were significantly protected against the challenge infection as evidenced by significantly lower mean parasitemia, lessened signs of acute disease, and reduced mortality than that observed in untreated controls. Mice receiving 5 weekly immunizing injections of irradiated parasites were more resistant to challenge than those receiving 3 in previous work. Mice receiving 8 weekly immunizing injections were not significantly more protected against challenge than those receiving 5. Mice given 5 weekly injections of 20·0 × 10 6 irradiated parasites were significantly more resistant to challenge than those receiving 2·0 × 10 6 irradiated parasites on the same schedule. Mice given 5 weekly intraperitoneal injections of 20·0 × 10 6 irradiated parasites were significantly more resistant to challenge than those receiving an equivalent number of immunizing injections via the subcutaneous route.

Primaquine analogues that are potent anti-Trypanosoma cruzi agents in a mouse model.

Seventy-seven primaquine analogues were evaluated for their effectiveness in reducing the parasitaemias in female albino mice (aged 4-6 weeks) which had been infected with a Brazilian strain of Trypanosoma cruzi 15 days earlier. Of the analogues tested, 23 were more effective than the reference drug, nifurtimox, and one was > 14-fold as effective as the standard and almost four times as active as primaquine itself. Certain members of the series tested warrant further evaluation.

The influence of gonadectomy of host on parasitemia and mortality of mice infected with Trypanosoma cruzi.

Male CF1 mice were more susceptible to acute infections of Trypanosoma cruzi than female mice as evidenced by significantly greater maximum mean parasitemia of approximately 8.9 times 10-6 per ml in males as compared to 1.5 times 10-6 per ml in females. Mortality was also greater in males (80 to 90% as compared to 28% in females). Ovariectomy of female mice made them more susceptible than unoperated female of similar age and stock to the Brazil strain of T. cruzi as indicated by maximum mean parasitemia of 10.9 times 10-6 per ml in the former and 7.5 times 10-6 in the latter. Mortality of the ovariectomized mice was as great as 90% in some experiments while that of unoperated controls nerve exceeded 30%. Parasitemia and mortality is castrated male mice were not significantly different from unoperated male mice infected with T. cruzi.

Leishmania donovani: Oral efficacy and toxicity of formycin B in the infected hamster

Formycin B, a structural analog of inosine, was evaluated as an orally administrable antileishmanial agent. Against Leishmania donovani in hamsters, it achieved an 85-92% reduction in numbers of parasites in livers of infected animals after oral administration at 13 mg/kg/day for 4 days. Its efficacy by oral administration was approximately four to eight times that by intramuscular administration and four times that of the positive control drug Glucantime by intramuscular administration. The levels of formycin B in serum after the final oral administration of 26 mg/kg/day were 1.4 micrograms/ml at 1 hr and 0.3 microgram/ml at 2 hr. The concentration in liver was greater (9.0 micrograms/ml at 1 hr) and declined more slowly. With this latter dosage or with 104 mg/kg/day there was no acute toxicity of formycin B to bone marrow or formed elements of the blood. The only statistically significant toxicity to the liver was a doubling of serum total bilirubin levels. Comparison of the in vivo efficacy of formycin B against L. donovani to the mild acute toxicity of the drug suggests that formycin B has potential as an oral agent against visceral leishmaniasis.

Development of Leishmania (viannia) panamensis lesions and relationship of numbers of amastigotes to lesion area on antimony-treated and untreated hamsters

Young adult (60-70-g) male golden hamsters (Mesocricetus auratus) each were injected intradermally at the dorsal base of the tail with 15 x 10(6) promastigotes of Leishmania (Viannia) panamensis (MHOM/PA/83/WR539), and progression and regression of subsequent lesions were evaluated for up to 17 wk postinfection (PI) as to area, weight, and number of amastigotes within lesions in untreated hamsters and in hamsters treated with meglumine antimoniate (Glucantime). In untreated hamsters total area of lesion, weight, and numbers of amastigotes generally increased rapidly and concomitantly up to 3-4 wk PI. Amastigote numbers tended to decrease from 4 to 11 wk PI and subsequently the numbers of amastigotes within the lesions decreased rapidly, whereas relatively little change occurred in the area and weight of the lesions. Meglumine antimoniate treatment of cutaneous hamster lesions resulted in marked concomitant decrease in size of the lesions and numbers of amastigotes within the lesions examined 1 wk after treatment. Measurement of the area of cutaneous leishmanial lesions thus would appear to be a valid method of evaluating the efficacy of promising compounds against L. panamensis in hamsters when measurements are taken 3-5 wk after experimental infection and reflects the number of amastigotes present in the lesion.

Relative Insensitivity of a Kenyan Strain of Leishmania donovani to Pentavalent Antimony Therapy in Hamsters

racidium and the eggshell retained stainability with immunofluorescence (Fig. 2). When nonheated sections were used for titration of sera by the IIF technique, the titer differed at different sites on the sections (Table II). The intraoval space showed stainability at higher dilutions than miracidia or host tissues. The positive titers against the antigen in this space ranged from 1: 80 to 1: 2,560. These titers were much higher than those measured by the COP test. When autoclaved sections were used, the titers of these sera against the antigen in the intraoval space were reduced at least fourfold. Furthermore, there seemed to be a correlation between the COP titer and the IIF titer detected on the autoclaved sections. Using histochemical techniques, Smith and von Lichtenberg(1967, Am. J. Pathol. 50:933-1007) have demonstrated a variety of substances associated with the contents of S. mansoni eggs, and they reported the existence of periodic acidSchiff (PAS) positive materials in the space beracidium and the eggshell retained stainability tween the miracidium and the eggshell. Booter et al. (1979, J. Immunol. 122: 39-43) isolated a polysaccharide antigen from S. mansoni eggs. Similarly, Long et al. (1981, Infect. Immun. 34: 389-396) obtained glycoprotein fractions from crude egg antigens of S. japonicum that contained COP inhibitory activity. We have demonstrated that there was amylase-resistant PAS positive material in the intraoval space of S. japonicum where the stainability by IIF technique was retained after autoclaving. We also demonstrated that the stainability with PAS was not altered by autoclaving (Fig. 3). These results show that the heat-stable antigen taking part in the COP reaction is most probably a polysaccharide and is located in the area between the miracidium and the eggshell. Infections of rabbits with S. japonicum and collections of the sera were done at the Schistosomiasis Control and Research Project (SCRP), Palo, Leyte, Philippines, for which we thank their staff.

Evidence that certain 8-aminoquinolines are potentially effective drugs against Chagas disease

Forty 8-aminoquinolines (a chemical class with members having some activity against Trypanosoma cruzi infections) were evaluated for their effectiveness in reducing the 14-day parasitaemias of 4-6 week-old, female, albino mice infected with a Brazilian strain of T. cruzi. Six of the compounds were more active or as active as the reference drug, nifurtimox, and one was > 13-fold as efficacious. Certain members of the series tested warrant further evaluation.