An improved procedure for the purification of Trypanosoma cruzi (Chagas, 1909) metacyclics from the insect vector

Activity in vivo of anti-Trypanosoma cruzi compounds selected from a high throughput screening

Novel technologies that include recombinant pathogens and rapid detection methods are contributing to the development of drugs for neglected diseases. Recently, the results from the first high throughput screening (HTS) to test compounds for activity against Trypanosoma cruzi trypomastigote infection of host cells were reported. We have selected 23 compounds from the hits of this HTS, which were reported to have high anti-trypanosomal activity and low toxicity to host cells. These compounds were highly purified and their structures confirmed by HPLC/mass spectrometry. The compounds were tested in vitro, where about half of them confirmed the anti-T. cruzi activity reported in the HTS, with IC50 values lower than 5 µM. We have also adapted a rapid assay to test anti-T. cruzi compounds in vivo using mice infected with transgenic T. cruzi expressing luciferase as a model for acute infection. The compounds that were active in vitro were also tested in vivo using this assay, where we found two related compounds with a similar structure and low in vitro IC50 values (0.11 and 0.07 µM) that reduce T. cruzi infection in the mouse model more than 90% after five days of treatment. Our findings evidence the benefits of novel technologies, such as HTS, for the drug discovery pathway of neglected diseases, but also caution about the need to confirm the results in vitro. We also show how rapid methods of in vivo screening based in luciferase-expressing parasites can be very useful to prioritize compounds early in the chain of development.

Chagas is a devastating disease affecting about 100 million people in Latin America. The drugs available for treatment against the causative agent, the parasite Trypanosoma cruzi, have associated toxicity and are not completely effective against the chronic form of the disease, which is the most common presentation in the clinic. There is a great need for new drugs against this disease. Novel technologies in drug development are now being applied for the search of new compounds against Chagas. Taking advantage of a high throughput screening performed recently to identify compounds active against T. cruzi replication in host cells in vitro, we have selected 23 compounds, which have been re-tested to selected active ones. We have also adapted a transgenic T. cruzi expressing luciferase, which allows for direct visualization when mice are infected. These parasites have been used to establish a model for acute Chagas disease useful for drug testing in mice. Using this method, we have tested the activity of the selected compounds and found two compounds with strong anti-T. cruzi activity in mice.

Rapid isolation of metacyclic trypomastigotes of Trypanosoma cruzi from feces and urine of the vector

Metacyclic trypomastigotes of Trypanosoma cruzi from infected Triatoma infestans were isolated and purified by an improved procedure. By using feces and urine of bugs the duration and the number of steps for purification were greatly reduced, thereby minimizing any possible effects on the flagellates. After DEAE-Sephacel column chromatography, a buffer supplemented with bovine serum albumin protected against the slight surface alterations of the trypomastigotes otherwise observed. About 10(7) metacyclic trypomastigotes (including 30% intermediate flagellates) were obtained from 100 bugs. The intermediate forms possessed the surface charge of trypomastigotes, and the kinetoplast was beside or posterior to the nucleus but not subterminal. Further increases in the number of bugs and the purified trypomastigotes were also possible with only slight increases in the time needed for isolation. In a comparison of complement-mediated lysis resistance and infectivity for mice, pre- and post-separation trypomastigotes showed no significant differences.

Immunization and challenge of mice with insect-derived metacyclic trypomastigotes of Trypanosoma cruzi

Infection with Trypanosoma cruzi was established in the reduviid vector, Dipetalogaster maximus, by repeated feedings on mice with high parasitaemias, and metacyclic trypomastigotes (IMT) were collected in insect urine after blood meals. The infectivity of IMT in mice was assessed by placing varying numbers of organisms, ranging from 5 to 5000, on to the conjunctivae or oral mucosa of anaesthetized animals. Half of the mice exposed to as few as 20 IMT by either route became parasitized, and the minimum inoculum size that resulted in all mice becoming infected was 640 IMT by the ocular route and 1250 IMT in the mice given parasites by mouth. Mice were immunized by tail vein infusion of irradiated IMT. Animals in the immunized group and in two control groups were then challenged by deposition of IMT on to the oral mucosa. Two of five immunized mice and nine of 10 comparison animals developed acute T. cruzi infection after challenge. These results indicate that IMT produced in this system are highly infective and that inocula containing 500-1000 IMT applied to the conjunctivae or oral mucosa constitute a gentle contaminative challenge. Moreover, our findings suggest that sterile protection against a contaminative challenge may be inducible by immunization with IMT, but experiments involving larger numbers of animals must be performed to resolve this question.

Trypanosoma cruzi: a specific surface marker for the amastigote form

Among the known life cycle stages of Trypanosoma cruzi only the amastigote form bound lactoferrin (LF), a glycoprotein produced by neutrophils. This capacity was readily demonstrable by indirect immunofluorescence in amastigotes derived from mice, a mammalian cell culture, or grown in an axenic medium. No LF binding was detectable on trypomastigotes from blood or mammalian cells, insect-derived metacyclics or epimastigotes, or on epimastigotes grown in Warren's medium. Serum levels of LF were increased in mice acutely infected with T. cruzi, and amastigotes from the spleens of these animals were found to have the glycoprotein on their surface. The amastigote LF receptor may have biological significance in parasite-host interaction since mononuclear phagocytes also express a LF receptor, and treatment of these cells with LF has been shown to increase their capacities to take up and kill T. cruzi amastigotes in vitro. The LF receptor is the first marker for T. cruzi amastigotes for which a naturally occurring ligand has been described.