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iological activity of 1,2,3,4-tetrahydro-�-carboline-3-carboxamidesgainst Trypanosoma cruzi
odrigo Hinojosa Valdeza, Lilian Tatiani Düsman Toninb, Tânia Ueda-Nakamurac,enedito Prado Dias Filhoa,c, José Andrés Morgado-Diazd,aria Helena Sarragiottob, Celso Vataru Nakamuraa,c,∗
Programa de Pós-graduacão em Microbiologia, Universidade Estadual de Londrina, Rodovia Celso Garcia Cid, PR 445, Km 380,ampus Universitário, CEP 86051-990 Londrina, Paraná, BrazilDepartamento de Química, Universidade Estadual de Maringá, Av. Colombo 5790, CEP 87020-900 Maringá, Paraná, BrazilDepartamento de Análises Clínicas, Laboratório de Microbiologia Aplicada aos Produtos Naturais e Sintéticos, Bloco I-90 Sala 123 CCS,niversidade Estadual de Maringá, Av. Colombo 5790, CEP 87020-900 Maringá, Paraná, BrazilDivisão de Biologia Celular, Instituto Nacional do Câncer, Rio de Janeiro, RJ, Brazil
r t i c l e i n f o
rticle history:eceived 6 June 2008eceived in revised form 4 October 2008ccepted 12 November 2008vailable online 20 November 2008
a b s t r a c t
Several �-carboline compounds were evaluated for in vitro trypanocidal activity against Trypanosomacruzi and their potential toxic effects was also assessed. �-Carboline derivative 4 showed good activityagainst epimastigote, trypomastigote, and amastigote forms of T. cruzi, with a dose-dependent inhibitoryeffect. It showed an IC50 of 14.9 �M against the epimastigote form and an EC50 of 45 �M and 33 �M againsttrypomastigote and amastigote forms, respectively. Additionally, 4 was able to be active on mammaliancell–protozoan interaction, reducing the number of infected cells and the number of internalized para-
sites. The compound showed low cytotoxicity, with a selective index 31 times higher to the parasite thanfor mammalian cells. In human red-blood cells �-Carboline 4 at 14.9 �M not caused haemolysis. Observedat electron microscopy 4-treated epimastigotes showed abnormal swelling of the mitochondrion, a dif-fuse kinetoplast, and distortions of the parasite cell body. The present data support the potential effect ofthis class of compounds against T. cruzi and encourage further experiments in vitro to evaluate the action
nd al
mechanism of this drug a
. Introduction
Chagas’ disease, also called American trypanosomiasis, is a par-sitic disease caused by the kinetoplastid protozoan TrypanosomaSchizotrypanum) cruzi. It is endemic from Mexico to Argentine, andfflicts 16–18 million people. Mortality rates range from 8% to 12%epending on the age and physiological state of the patient (WHO,002).
The current treatment for this disease is very limited, and no suc-essful vaccine has been developed (Maya et al., 2007). The available
rugs for clinical treatment are the nitroderivatives Benznidazolend Nifurtimox, both unsatisfactory. These drugs have variable ther-peutic effects, according to the geographical region, and requireong-term treatment, besides frequently having toxic side effects.
∗ Corresponding author at: Universidade Estadual de Maringá, Departamento denálises Clínicas, Laboratório de Microbiologia Aplicada aos Produtos Naturais eintéticos, Bloco I-90 Sala 123 CCS, Avenida Colombo, 5790, BR-87020-900 Maringá,R, Brazil. Tel.: +55 44 3261 4863; fax: +55 44 3261 4860.
They are only effective against the acute infection, during whichmost patients do not know that they are infected with T. cruzi. Inaddition, they have limited efficacy in the chronic stage (Coura andDe castro, 2002). Furthermore, important differences in suscepti-bility to these drugs have been detected among different parasitestrains isolated in various parts of the Americas (Rivas et al., 1999).
A number of new drugs have been reported to be effective invitro or in vivo against T. cruzi, but none has been found to be com-pletely satisfactory, for either the treatment of Chagasic patientsor for prophylaxis of blood to prevent infection via blood transfu-sion. Clearly, new drugs and new approaches for confronting theseproblems are necessary (Bernacchi et al., 2002). In this context,an exhaustive search for new synthetic and natural products fortreatment of Chagas disease is ongoing (Croft et al., 2005). The �-carbolines, which are widespread in nature and have been isolatedfrom fungi, higher plants, marine organisms, and mammals, have
shown good activity against T. cruzi (Rivas et al., 1999).
Natural and synthetic �-carbolines and tetrahydro-�-carbolinealkaloids are well-known compounds that possess several bio-logical properties, such as anticonvulsive, ansiolytic, sedative,antimicrobial, antithrombotic, anti-HIV, antiproliferative, insecti-
idal, and parasiticidal (Ishida et al., 2001; Lin et al., 2002; Castro etl., 2003; Takasu et al., 2004; Cao et al., 2005; Costa et al., 2006).
This class of compounds has been tested in trypanocidal assays,nd some reports have shown the activity of �-carbolines andetrahydro-�-carbolines against T. cruzi (Calvin et al., 1987). In arevious work we demonstrated the activity of 1-(nitrophenyl)-etrahydro-�-carbolines against epimastigote forms of T. cruziTonin et al., 2008).
In the present study, a series of 12 1-substituted-1,2,3,4-etrahydro-�-carboline-3-carboxamides was synthesized andcreened for antitrypanosomal activity against epimastig-te form of T. cruzi. The effect of the most active compound-butyl-1-(4-dimethylamino)phenyl-1,2,3,4-tetrahydro-�-arboline-3-carboxamide (4) was evaluated against amastigote,nd trypomastigote forms of T. cruzi also.
. Materials and methods
.1. Chemistry
The aldehydes and amines used in this study were purchasedrom Sigma–Aldrich (Saint Louis, USA), Acros-Organics (Geel,elgium) and Merck (Darmstadt, Germany). l-Tryptophan was pur-hased from Synth (São Paulo, Brazil) and trifluoroacetic acid (TFA)as obtained from Carlo Erba (Milan, Italy).
The compounds were characterized by the mass spectra (EIMS)btained on Shimadzu-CG/MS model QP 2000A spectrometer, NMRpectra data, recorded in a Varian spectrometer model Mercurylus BB 300 MHz, and (IR) spectra (KBr) recorded on a Bomempectrophotometer, MB-100 model.
.2. General procedure for synthesis of-carboline-3-carboxamides 4–15
The tetrahydro-�-carboline-3-carboxamides were preparedrom l-tryptophan 1, through a Pictet-Spengler condensationBailey et al., 1987), of the l-tryptophan methyl ester 2 with aeries of aromatic aldehydes, followed by the reaction of the methyletrahydro-�-carboline-3-carboxylate intermediates with differentmines, according to the procedure previously reported (Coutts etl., 1984).
The N-butyl-1-(4-dimethylamino)phenyl-1,2,3,4-tetrahydro--carboline-3-carboxamide 4 was obtained from the reactionf the corresponding ester 3 with butylamine (Fig. 1).
mixture of l-tryptophan methyl ester 2 (0.5 mmol), 4-imethylaminobenzaldehyde (0.5 mmol) and trifluoroaceticcid (trace) in CH2Cl2 (10 mL) was stirred at 0 ◦C, over molecular
ieves. After 24 h, an excess of TFA (1.0 mmol) was added, and theixture was stirred at room temperature for 6 h, followed by evap-
ration of the solvent. Treatment of the crude product with 10%a2CO3, extraction with EtOAc (3× 10 mL), drying of the organic
ayer under anhydrous Na2SO4, filtration and solvent evaporation
ig. 1. General procedure for the synthesis and general chemical structure of N-butyl-1-(4-nd conditions: (a) H3COH, H2SO4, reflux, 12 h; (b) 4-dimethylaminobenzaldehyde, CH2Cl2eflux, 24 h.
ica 110 (2009) 7–14
afforded a residue which was purified on a chromatographiccolumn (silica flash; hexane-EtOAc 20%) to give the compound 3as a cis/trans mixture.
A solution of methyl-1-(4-dimethylamino)phenyl-1,2,3,4-tetrahydro-�-carboline-3-carboxylate 3 (1.0 mmol) andbutylamine (5 mL) was refluxed for 24 h; then the excess aminewas removed under vacuum. The residue was crystallized by usingMeOH as a solvent, to give the compound 4 as a cis/trans mixture.The synthesized compound was characterized by spectral (1H and13C NMR, MS and IR) data. The stereochemistry of cis and transisomers was assigned on the basis of 13C NMR data (Düsman et al.,2005).
2.3. Parasite
The epimastigote form of T. cruzi Y strain was grown in Liver Infu-sion Tryptose (LIT) supplemented with 10% foetal calf serum (FCS,Gibco, Invitrogen Corporation, New York, USA) at 28 ◦C for 96 h.Trypomastigote and amastigote forms were obtained by infectionof LLCMK2 cell monolayer in Dulbecco’s modified Eagle’s medium(DMEM, Gibco Invitrogen Corporation, New York, USA) at 37 ◦C and5% CO2 atmosphere.
2.4. Cell culture
LLCMK2 (monkey kidney cells) were maintained in DMEM sup-plemented with 2 mM l-glutamine, 10% FCS, 50 mg/L gentamicinand buffered with sodium bicarbonate.
2.5. Antiproliferative activity of ˇ-carboline 4 on theepimastigote form
The epimastigote form of T. cruzi in the logarithmic phase wasused for this assay. The �-carboline compounds were dissolvedin dimethylsulfoxide (DMSO) and LIT medium to obtain concen-trations of 3 �M, 13 �M, 26 �M, 128 �M and 256 �M. The finalconcentration of DMSO did not exceed 1%. For each experiment,there was a growth control with and without DMSO.
A cell density of 1 × 106 epimastigotes/mL was cultured in a 24-well microplate to obtain a final volume of 1 mL. The cells wereincubated at 28 ◦C and their growth was determined by countingthe parasites with a haemocytometer chamber every day for 7 days.The IC50 values (50% inhibition concentration) were determinedusing linear regression analysis from this inhibition percentage.Benznidazole-Rochagan® (Roche Pharmaceuticals, Rio de Janeiro,Brazil) was used as the reference drug.
2.6. Effect of ˇ-carboline 4 on the viability of the trypomastigoteand amastigote forms
The tissue-culture-derived parasite trypomastigote andamastigote forms were resuspended in Dulbecco’s modified
mastigotes caused progressive parasite injury, compared with theuntreated cells, and a dose-dependent effect was observed. After
R.H. Valdez et al. / Ac
agle medium supplemented with FCS containing 10% mouselood in a concentration of 107 parasites/mL. In a 96-wellicroplate, 100 �L of this suspension was added to the same
olume of the drug diluted in DMSO and DMEM at twice theesired final concentration (8 �M, 16 �M, 32 �M, 64 �M, 128 �M,56 �M, 513 �M, 1026 �M and 2051 �M), and incubated for4 h at 37 ◦C. Considering the mobility of this form of parasite,hich permit distinguishes his viability, we used the Pizzi-Brenerethod. For this an aliquot of 5 �L of each sample were placed
n slides plus coverslips and immediately counted in an opticalicroscopy (Brener, 1962), subsequently the EC50 (concentra-
ion which lysed 50% of the parasites) was calculated. In thease of amastigote forms where is impossible to distinguishhe mobility of viable and unviable cells, the viability of freemastigotes was determined by counting in a haemocytometerhamber (Improved Double Neubauer) with a light microscope,fter addition of 0.4% erythrosine B. Crystal violet (Inlab, São Paulo,razil) was used as the reference drug. The EC50 value was alsovaluated.
.7. Effect of ˇ-carboline 4 on the intracellular amastigote in theLCMK2 cell line
In the 24-well microplate containing glass coverslips, a 500 �Lliquot of the LLCMK2 cells (2.5 × 105 cells/mL) was seeded inach well and incubated for 24 h at 37 ◦C with 5% CO2. Next,he LLCMK2 cell monolayer was infected with trypomastigotes10:1) for 24 h, then washed with 0.01 M phosphate-buffered salinePBS) pH 7.2, and fresh medium with and without the drugn different concentrations (16 �M, 32 �M, 64 �M and 128 �M)as added to the wells. The microplate was incubated for 96 h
t 37 ◦C with 5% CO2 atmosphere. The cells were fixed withethanol and stained with May-Grunwald-Giemsa (Gibco, Invit-
ogen Corporation, New York, USA) for 20 min, then the glassoverslips were permanently prepared with Entellan® (Merck,armstadt, Germany). The percentage of infected cells and theumber of intracellular parasites were estimated by observing00 cells with a light microscope (Olympus CX31), and the sur-ival index (product of the percentage of cells infected and theumber of amastigotes per cell) and EC50 value (effective con-entration) were determined. Benznidazole was used as referencerug.
.8. Ultrastructural analysis
.8.1. Transmission electron microscopyEpimastigote forms of T. cruzi, after treatment with 14.9 �M
IC50) of �-carboline 4, were harvested by centrifugation, washedn PBS and fixed in 2.5% glutaraldehyde in 0.1 M cacodylate bufferH 7.2 for 1 h at 4 ◦C. Next, the cells were post-fixed in a solutionontaining 1% OsO4, 0.8% potassium ferrocyanide and 10 mM CaCl2n 0.1 M cacodylate buffer at room temperature for 60 min, washed
ith 0.1 M cacodylate buffer, dehydrated in ethanol, and embeddedn Epon® resin. Ultrathin sections were stained with uranyl acetatend lead citrate and observed with a Zeiss EM900 transmissionlectron microscope.
.8.2. Scanning electron microscopyEpimastigote and trypomastigote forms of T. cruzi treated
ith �-carboline 4 at IC50 and EC50 values respectively were
xed with 2.5% glutaraldehyde in 0.1 M cacodylate buffer forh at room temperature, washed three times in cacody-
ate buffer and adhered on poly-l-lysine coated coverslips.ext, the parasites were dehydrated in an ascending ethanol
eries, critical-point dried with CO2, sputter-coated with gold,
ica 110 (2009) 7–14 9
and observed in a Shimadzu SS-550 scanning electron micro-scope.
2.9. Cytotoxicity assay
The LLCMK2 cells were seeded onto 96-well microplates at aconcentration of 2.5 × 105 cells/mL and incubated for 24 h in DMEMsupplemented with 10% FCS. The monolayer obtained was treatedwith different concentrations of �-carboline (25 �M, 128 �M,256 �M and 1282 �M). DMSO was used as a negative control, andBenznidazole was used as the reference drug. After incubation at37 ◦C with 5% CO2 for 96 h, cell viability was evaluated by the sul-forhodamine B technique (Skehan et al., 1990). The absorbance wasread at 530 nm in a microplate spectrophotometer (Biotek-PowerWave XS). Next, the CC50 of the drug (concentration of drug thatlysed 50% of cells) was calculated.
2.10. Red blood cell lysis assay
The potential haemolytic effect of �-carboline was evaluatedin this assay. A 4% suspension of fresh defibrinated human bloodwas prepared in sterile 5% glucose solution. One of several concen-trations (3 �M, 13 �M, 26 �M, 126 �M, 256 �M and 1282 �M) ofthe �-carboline compound was added to each test tube and gentlymixed, and the tubes incubated at 37 ◦C. After 1 h of incubation, thevisual reading was made, and after 2 h the samples were centrifugedat 1000 × g for 10 min. The absorbance of the supernatant was deter-mined at 540 nm for estimation of haemolysis. The results wereexpressed as percentage of haemolysis, by the equation Haemoly-sis: (%) = 100 − [(Ap − As)/(Ap − Ac) × 100]; where Ap, As and Ac arethe absorbance of the positive control, test sample and negativecontrol, respectively. Amphotericin B (Cristalia, São Paulo, Brazil)was used as the reference drug, Triton X-100 (Vetec, Rio de Janeiro,Brazil) was used as the positive control, and the cell suspension onlywas used as the negative control.
2.11. Statistical analysis
Statistical analysis was done with the program GraphPad Prism4 (GraphPad Software, San Diego, California, USA). Student’s t-testwas applied and a p-value less than 0.05 was regarded as signifi-cant. The experiments were performed in triplicate, in at least threeindependent experiments.
3. Results
3.1. Effects of ˇ-carboline 4 on growth of the epimastigote form
Some �-carboline compounds showed good activity againstthe proliferation of epimastigotes, which is the form present inthe reduviid vector. Comparison of the 50% inhibition concen-tration values (IC50 in �M) for antitrypanosomal activity of 12compounds synthesized showed that the compound bearing a 4-dimethylaminophenyl and an N-butylcarboxamide group in the 1-and 3-positions of the tetrahydro-�-carboline ring (compound 4,Fig. 1) showed the most activity, with IC50 of 14.9 �M (Table 1).
The presence of �-carboline 4 in the culture of Y-strain epi-
96 h of incubation with 256 �M of the compound (the high-est concentration tested), growth was completely arrested. TheIC50 and the IC90 values of �-carboline 4 were 14.9 ± 6.5 �M and76.9 ± 13.2 �M, respectively (Fig. 2). IC50 to Benznidazole was7.7 ± 2.9 �M.
Table 1General structure for �-carbolines and its IC50 (�M) values for 1-substituted-1,2,3,4-tetrahydro-�-carboline-3-carboxamides (4–15) against T. cruzi epimastigotes.
R1 R2 Isomer IC50
4 cis + trans 14.9
5 trans >100
6 trans 79.6
7 cis + trans 33.9
8 cis 49.6
9 cis >100
10 cis >100
11 cis >100
12 cis + trans 24.4
13 cis + trans >100
14 cis 28.1
1
3a
tdta2
pAwvo
3L
s
5
.2. Effect of ˇ-carboline 4 on the viability of the trypomastigotend amastigote forms
We evaluated the activity of �-carboline 4 on the viability of therypomastigote and amastigote forms. A lytic activity with a dose-ependent trypanocidal effect was observed (Table 2). Against therypomastigote form, in the presence of mouse blood, was observed50% effective concentration (EC50) of 45 ± 3.9 �M, at 37 ◦C after
4 h.In the amastigote form, the highest concentration of the com-
ound tested was 256 �M and showed a good lytic effect at 37 ◦C.fter 24 h of treatment, in the presence of mouse blood the EC50as 33 ± 5.6 �M (Table 2). The effect of the reference drug, crystal
iolet, against trypomastigote and amastigote forms showed EC50f 12.8 ± 2.6 �M and 6.7 ± 2.1 �M, respectively.
.3. Effect of ˇ-carboline 4 on the intracellular amastigote in theLCMK2 cell line
The treatment of LLCMK2 infected with amastigote formshowed that the compound had good activity, with a dose-
trans >100
dependent trypanocidal effect (Fig. 3), leading to considerablereduction in both the percentage of infected cells and the mean ofnumber of parasites per infected cells. After 96 h of incubation, thepercentage of LLCMK2 cells with internalized parasites was higherfor the control than for cells infected and treated with �-carboline4 (Fig. 3). At that time, the control showed a mean 31.9 amastigotesper cell and 72% of cells infected. Cells treated with 32 �M showeda mean 4.9 internalized amastigotes, with 45% of cells infected.Treatment of the cells with 128 �M resulted in only 11% infectedcells and 2.1 parasites per cell. The effective concentration (EC50)against intracellular amastigotes was 20.2 ± 3.5 �M, meanwhile theEC50 value for Benznidazole was 26.1 �M. C4 also showed a lowervalue of SI50 at 17.5 �M (survival index of 50%) when compared withBenznidazole with SI50 at 28.7 �M.
3.4. Ultrastructural effects
3.4.1. Transmission electron microscopyElectron microscopy analysis of epimastigote forms treated with
14.9 �M (IC50) of �-carboline 4, showed alterations of the typicalmorphology of the parasite, such as: swelling of the mitochondrion,
The values (�M) of IC50 represent the 50% inhibition concentration against epi-mastigote forms (28 ◦C), EC50a the 50% effective concentration on trypomastigote
iffuse kinetoplasts, electron lucent reservosomes, and appearancef vacuoles (Fig. 4).
.4.2. Scanning electron microscopyMorphological alterations in the epimastigote and trypomastig-
te forms treated with �-carboline 4 were visualised by scanninglectron microscopy. In epimastigotes, the IC50 (14.9 �M) caused
istortions of the parasite cell body such as rounding and swelling ofell body, and a shortening of the flagellum (Fig. 5). In trypomastig-te forms treated with EC50 (45 �M), the alterations observed inhe cell body were loss of the normal shape and a reduction in theize of the flagellum (Fig. 5).
ig. 3. (a) Effect of �-carboline 4 on the Trypanosoma cruzi–LLCMK2 cell interaction. LLCMsurvival index, percent) was calculated by the equation (P2/P1) × 100, where P1 is the SI fercentage of LLCMK2 cells with internalized parasites and the mean number of internalixperiments. (b) Light microscopy of intra-cellular amastigotes and their interaction with Lith 32 �M and (C) cells treated with 128 �M; Bars = 10 �m.
forms (37 C), EC50b 50% effective concentration on amastigote forms (37 C), EC50c
50% effective concentration on mammalian cell–parasite interaction, CC50 refers to50% citotoxical concentration on LLCMK2 (37 ◦C) and HC50 refers to 50% haemolyticconcentration of red blood cells (37 ◦C).
3.5. Cytotoxic effect of ˇ-carboline 4 on LLCMK2 cells
This assay evaluated the potential toxic effects of this drug onthe LLCMK2 lineage, after 96 h of treatment. The cells treated with
256 �M led to 38.7% cellular inhibition. With 128 �M the cellularinhibition was 18.4%. The 50% cytotoxic concentration (CC50) was462 ± 112.1 �M (Table 2). The cytotoxic effects on LLCMK2 cells andactivity against the parasite were compared by using the selectivityindex (SI), ratio (CC50 for LLCMK2/IC50 for parasite). The �-carboline
K2 cells were infected with trypomastigote forms and treated with �-carboline 4. SIor the control and P2 is the SI for treated cells. SI was calculated by multiplying thezed parasites per cell. The data represent the mean values from three independentLCMK2 cells treated with �-carboline 4 for 96 h. (A) Untreated cells, (B) cells treated
Fig. 4. Transmission electron microscopy of Trypanosoma cruzi epimastigotes (Y strain) treated with �-carboline 4 for 96 h. (a) Control parasite showing characteristico FP). (b( (c) Anw
cm
3
b�al5hus(
4
sudoMecA
rganelles: the kinetoplast (K), nucleus (N), reservosome (R) and flagellar pocket (arrowhead), with a vacuole present in cytoplasm (V) and altered reservosomes (R).ith interruption in mitochondrial membrane (star). Bars = 1 �m.
ompound was more selective against the parasite than the mam-alian cells, with an SI of 31.
.6. Haemolytic assay
In this experiment we evaluated the toxicity for human red-lood cells of �-carboline 4 incubated at 37 ◦C for 120 min.-Carboline 4 at 14.9 �M (IC50) caused only 2.2% haemolysis, andt the highest concentration tested (1282 �M) caused only 28%ysis, therefore, the HC50 (haemolytic concentration that causes0% of lysis) was not calculated. Amphotericin B showed a strongaemolytic effect, with 70% haemolysis at 14.9 �M. Triton X-100sed as a positive control was considered 100% lysis, Benznidazolehowed low levels of haemolysis, and 1% DMSO did not cause lysisTable 2).
. Discussion
In the investigation of new trypanocidal compounds, manyources have been chosen, including natural and synthetic prod-cts. Natural products or derivatives play an important role in theevelopment of all types of drugs and some natural compounds
r extracts have shown trypanocidal activity (Paveto et al., 2004;esquita et al., 2005; Luize et al., 2006a; Dantas et al., 2006; Izumi
t al., 2008). In additional to the natural products, some syntheticompounds presented activity against T. cruzi (Garzoni et al., 2004;dade et al., 2007; Menna-Barreto et al., 2005; Bisaggio et al., 2008).
–d) Epimastigotes treated with �-carboline 4 at 14.9 �M. (b) A diffuse kinetoplastaltered mitochondrion (arrow). (d) A large vacuole (V) and a coiled mitochondrion
Furthermore some drugs used for the treatment of diseases causedby other microorganisms, such as fungal diseases, have been testedagainst T. cruzi (Urbina et al., 2000).
Although �-carbolines are widespread in nature and have beenisolated from many sources, only a few reports on their trypanoci-dal activity have appeared. Some earlier papers have reportedantimicrobial, antiproliferative, insecticidal, and parasiticidal activ-ity of �-carbolines (Cao et al., 2005). The results obtained in thepresent study showed that treatment of epimastigotes with chemi-cally modified �-carboline 4 for 7 days resulted in dose-dependentgrowth inhibition. In the first 24 h the compound already showeda significant inhibitory effect at 256 �M (p < 0.05). After 96 h,concentrations above 26 �M showed significant antiproliferativeactivity compared to the growth of the control (p < 0.01), andwith 256 �M growth was completely arrested. Transmission elec-tron microscopy analysis of epimastigotes treated with IC50 of�-carboline 4 demonstrated swelling of the mitochondrion and thepresence of vacuoles and a diffuse kinetoplast, while the cytoplas-mic membrane remained preserved. These alterations were alsofound in T. cruzi treated with other synthetic compounds such asrisedronate, in which mitochondrial swelling was among the mostprominent ultrastructural alterations seen in both epimastigote
and amastigote forms (Garzoni et al., 2004). Additionally, scan-ning electron microscopy study showed that epimastigotes treatedwith �-carboline 4 had some distortions on their surface, such asrounding and swelling of the cell body, and a reduction in the sizeof the flagellum compared to control cells. However, the plasma
ig. 5. Scanning electron microscopy of Trypanosoma cruzi epimastigotes (a–c) andhe typical elongated body with terminal flagellum. (b and c) Epimastigotes treatrypomastigotes treated with 45 �M for 24 h, showing distortion in cell body, rear = 1 �m.
embrane and subpellicular microtubules seemed to be preserved.hese alterations are similar to those reported previously, such ashose caused by essential oil of Syzugium aromaticum (Dantas et al.,006) and eupomatenoid-5 isolated from Piper regnellii (Luize et al.,006b).
The �-carboline compound also showed activity against the try-omastigote form, it caused heavy damage and extensive lysing.
oncentrations above 16 �M showed significant activity comparedo the control test (p < 00.1). When observed in SEM, the cell surfaceas altered and the cells had a short flagellum. In free amastigotes
he situation was similar and all concentrations showed significantctivity compared with the control (p < 0.01). Against the clinically
omastigotes (d–f) treated with �-carboline 4. Control parasites (a and d) showingith 14.9 �M for 96 h, showing a rounded cell body and small flagellum. (e and f)on in size, and probable loss of intracellular material (e). (a–c) Bar = 2 �m. (d–f)
important form (the intracellular amastigote) there was a hugereduction in the number of infected cells as well as in the numberof intracellular amastigotes. The drug was able to penetrate into thehost cell and act on the confined parasite, with no significant dele-terious effects on the host cells. The EC50 value was 20.2 ± 3.5 �M,a minor index than presented by Benznidazole which was 26.1 �M,similar to presented by previous reports (Saraiva et al., 2007). Addi-
tionally, the SI50 of C4 (17.5 �M), was also lower than presented byBenznidazole (28.7 �M).
Cytotoxicity assays demonstrated that �-carboline 4 was 31times more toxic to the parasite than to the LLCMK2 lineage. Inthe haemolytic assay, �-carboline 4 showed only 28% haemolysis
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4 R.H. Valdez et al. / Ac
t 1282 �M (a concentration 72 times higher than the IC50 forpimastigotes).
Although the mechanism of action of �-carboline compoundss unknown, recent reports have documented their significantntiproliferative activity in tumoral cells, and there is evidence thathese compounds can intercalate DNA. It can be envisaged that the-carboline ring system, having a planar aromatic structure, couldtack in the base pairs of DNA, and such intercalation could con-ribute to the biological activity (Boursereau and Coldham, 2004).ther reports have shown that a high concentration of �-carbolineas able to induce apoptosis in vitro (Hans et al., 2005). Further-ore, inhibition of the respiratory chain seems to be an important
ction mechanism of the majority of the �-carbolines studied in theulahuen strain of T. cruzi (Rivas et al., 1999).
The present data show the potential effect of the �-carbolineerivative (4), against the three forms of T. cruzi. This supports fur-her screening of new analogs, and more in vitro and in vivo studiesf this drug. Such studies are necessary to increase understandingf the mode of action of this drug and the possibility that it cane used alone or in combination with other drugs for treatment ofhagas’ disease in the future.
cknowledgements
This study was supported through grants from DECIT/SCTIE/MSnd MCT by Conselho Nacional de Desenvolvimento Científico eecnológico (CNPq), Financiadora de Estudos e Projetos (FINEP),rograma de Núcleos de Excelência (PRONEX/Fundacão Araucária),nd Programa de Pós-graduacão em Microbiologia da Universidadestadual de Londrina.
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