Astaxanthin induces autophagy and apoptosis in murine melanoma B16F10-Nex2 cells and exhibits antitumor activity in vivo

Countless efforts have been made to prevent and suppress the formation and spread of melanoma. Natural astaxanthin (AST; extracted from the alga Haematococcus pluvialis) showed an antitumor effect on various cancer cell lines due to its interaction with the cell membrane. This study aimed to characterize the antitumor effect of AST against B16F10-Nex2 murine melanoma cells using cell viability assay and evaluate its mechanism of action using electron microscopy, western blotting analysis, terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) assay, and mitochondrial membrane potential determination. Astaxanthin exhibited a significant cytotoxic effect in murine melanoma cells with features of apoptosis and autophagy. Astaxanthin also decreased cell migration and invasion in vitro assays at subtoxic concentrations. In addition, assays were conducted in metastatic cancer models in mice where AST significantly decreased the development of pulmonary nodules. In conclusion, AST has cytotoxic effect in melanoma cells and inhibits cell migration and invasion, indicating a promising use in cancer treatment.

Biological characterization of Trypanosoma cruzi epimastigotes derived from trypomastigotes isolated from Brazilian chagasic patients

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T. cruzi TcII isolates from chagasic patients have distinct biological parameters.

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Isolates were more glucose-dependent than long-term cultivated Y strain parasites.

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Significant differences were observed on complex II and IV-supported respiration.

Chagas disease (CD), caused by Trypanosoma cruzi, occurs in several countries in Latin America and non-endemic countries. Heterogeneity among T. cruzi population has been the Achilles’ heel to find a better treatment for CD. In this study, we characterized the biochemical parameters and mitochondrial bioenergetics of epimastigotes differentiated from eight T. cruzi isolates (I1-I8) obtained from Brazilian CD patients. Molecular analysis of parasites DTUs grouped all of them as TcII. The profile of the growth curves in axenic cultures was distinct among them, except for I1 and I3 and I2 and I4. Doubling times, growth rates, cell body length, and resistance to benznidazole were also significantly different among them. All the isolates were more glucose-dependent than other T. cruzi strains adapted to grow in axenic culture. Mitochondrial bioenergetics analysis showed that each isolate behaved differently regarding oxygen consumption rates in non-permeabilized and in digitonin-permeabilized cells in the presence of a complex II-linked substrate. When complex IV-linked respiratory chain substrate was used to provide electrons to the mitochondrial respiratory chain (MRC), similarity among the isolates was higher. Our findings show that TcII epimastigotes derived from patients’ trypomastigotes displayed their own characteristics in vitro, highlighting the intra-TcII diversity, especially regarding the functionality of mitochondrial respiratory complexes II and IV. Understanding T. cruzi intraspecific biological features help us to move a step further on our comprehension regarding parasite's survival and adaptability offering clues to improve the development of new therapies for CD.

Evaluation of Trypanosoma cruzi parasitic load by real-time PCR and blood culture in long-term kidney transplant recipients

INTRODUCTION

Acute Chagas disease involving reactivation can occur after organ transplant, and follow-up by direct parasitological or molecular methods is essential for monitoring the parasitic load in such patients. In contrast, there is a little data on the parasitic load in long-term organ recipients. In this study, we examined the parasitic load in long-term kidney transplant patients and assessed the possibility of late Chagas disease reactivation.

METHODOLOGY

Blood cultures and real-time PCR were used to assess the parasitic load in four immunosuppressed patients who underwent kidney transplants (between 1996 and 2014) and were also treated for parasites.

RESULTS

There were no positive blood culture or real-time PCR results in Chagas disease patients who received kidney transplants. The real-time PCR presented detection limit of 0.1 parasite equivalent/mL. The time interval between the transplant and sample collection varied from one to 19 years.

CONCLUSIONS

No parasites were detected in the evaluated patients. The use of benznidazole and immunosuppressive therapy may have contributed to control the T. cruzi infection. In transplanted patients with Chagas disease, the use of methods such real-time PCR and blood culture can monitor the parasitic load and prevent disease reactivation.

Genotypic Trypanosoma cruzi distribution and parasite load differ ecotypically and according to parasite genotypes in Triatoma brasiliensis from endemic and outbreak areas in Northeastern Brazil

This study aimed to identify the Trypanosoma cruzi genotypes and their relationship with parasitic load in distinct geographic and ecotypic populations of Triatoma brasiliensis in two sites, including one where a Chagas disease (ChD) outbreak occurred in Rio Grande do Norte state, Brazil. Triatomine captures were performed in peridomestic and sylvatic ecotopes in two municipalities: Marcelino Vieira - affected by the outbreak; and Currais Novos - where high pressure of peridomestic triatomine infestation after insecticide spraying have been reported. The kDNA-PCR was used to select 124 T. cruzi positive triatomine samples, of which 117 were successfully genotyped by fluorescent fragment length barcoding (FFLB). Moreover, the T. cruzi load quantification was performed using a multiplex TaqMan qPCR. Our findings showed a clear ecotypic segregation between TcI and TcII harboured by T. brasiliensis (p<0.001). Although no genotypes were ecotypically exclusive, TcI was predominant in peridomestic ecotopes (86%). In general, T. brasiliensis from Rio Grande do Norte had a higher T. cruzi load varying from 3.94 to 7.66 x 10⁶T. cruzi per insect. Additionally, TcII (median value=299,504 T. cruzi/intestine unit equivalents) had more than twice (p=0.1) the parasite load of TcI (median value=149,077 T. cruzi/intestine unit equivalents), which can be attributed to a more ancient co-evolution with T. brasiliensis. The higher prevalence of TcII in the sylvatic T. brasiliensis (70%) could be associated with a more diversified source of bloodmeals for wild insect populations. Either TcI or TcII may have been responsible for the ChD outbreak that occurred in the city of Marcelino Vieira. On the other hand, a smaller portion of T. brasiliensis was infected by TcIII (3%) in the peridomicile, in addition to T. rangeli genotype A (1%), often found in mixed infections. Our results highlight the need of understanding the patterns of T. cruzi genotype´s development and circulation in insect vectors and reservoirs as a mode of tracking situations of epidemiologic importance, as the ChD outbreak recently recorded for Northeastern Brazil.

Mitochondrial behavior during nuclear and mitochondrial DNA repair in Trypanosoma cruzi epimastigotes

Different genotoxic agents can lead to DNA single- and double-strand breaks, base modification and oxidation. As most living organisms, Trypanosoma cruzi is subjected to oxidative stress during its life cycle; thus, DNA repair is essential for parasite survival and establishment of infection. The mitochondrion plays important roles beyond the production of ATP. For example, it is a source of signaling molecules, such as the superoxide anion and H₂O₂. Since T. cruzi has only one mitochondrion, the integrity of this organelle is pivotal for parasite viability. H₂O₂ and methyl methanesulfonate cause DNA lesions in T. cruzi that are repaired by different DNA repair pathways. Herein, we evaluate mitochondrial involvement during the repair of nuclear and mitochondrial DNA in T. cruzi epimastigotes incubated with these two genotoxic agents under conditions that induce repairable DNA damage. Overall, in both treatments, an increase in oxygen consumption rates and in mitochondrial H₂O₂ release was observed, as well as maintenance of ATP levels compared to control. Interestingly, these changes coincided with DNA repair kinetics, suggesting the importance of the mitochondrion for this energy-consuming process.

Prospecting and Identifying Phyllanthus amarus Lignans with Antileishmanial and Antitrypanosomal Activity

Ten lignans (1:  - 10: ) were isolated from the hexane-ethyl acetate extract of Phyllanthus amarus leaves. Three of them, cubebin dimethyl ether (3: ), urinatetralin (4: ), and lintetralin (7: ) are described for the first time in this species, while phyllanthin (1: ), niranthin (2: ), 5-demethoxyniranthin (5: ), isolintetralin (6: ), hypophyllanthin (8: ), nirtetralin (9: ), and phyltetralin (10: ) have been already reported from P. amarus. Among the lignans tested against Trypanosoma cruzi intracellular amastigotes, 2: was the most active with an EC₅₀ of 35.28 µM. Lignans 2, 5, 7: , and 9: showed inhibitory effects against Leishmania amazonensis promastigotes with EC₅₀ of 56.34, 51.86, 23.57, and 43.27 µM, respectively. During in vitro infection assays, 5: reduced amastigotes by 91% at 103.68 µM concentration, whereas 7: and 9: reduced amastigotes by approximately 84% at 47.5 and 86.04 µM, respectively. Lignans 5, 7: , and 9: were more potent in intracellular amastigotes with EC₅₀ of 2.76, 8.30, and 15.83 µM, respectively, than in promastigotes. CC₅₀ for all samples was > 100 µg/mL, thus revealing low cytotoxicity against macrophages, and selectivity against the parasite. L. amazonensis promastigotes treated with compounds 2: and 9: showed decreased respiratory control of 38% and 25%, respectively, suggesting a change in mitochondrial membrane potential and lower ATP production.

Using a Chagas disease hospital database: a clinical and epidemiological patient profile

INTRODUCTION

Chagas disease (CD) prevention and control rely on studies of its distribution, characteristics of individuals affected and mode of transmission. CD data in Brazil are scarce; a retrospective analysis of the clinical characteristics of 80 patients treated at the Clinical Hospital of UNICAMP, Campinas, Brazil, was performed.

METHODS

Patient data records were analyzed.

RESULTS

Thirty percent of the patients probably got infected through vector-borne transmission, 65% came from endemic areas, a predominance of cardiac and cardiodigestive forms was found among males, and the cardiac form prevailed (51%).

CONCLUSIONS

The results update the view on the epidemiology of CD in Campinas, Brazil.

Trypanosoma cruzi tryparedoxin II interacts with different peroxiredoxins under physiological and oxidative stress conditions

Trypanosoma cruzi, the etiologic agent of Chagas disease, has to cope with reactive oxygen and nitrogen species during its life cycle in order to ensure its survival and infection. The parasite detoxifies these species through a series of pathways centered on trypanothione that depend on glutathione or low molecular mass dithiol proteins such as tryparedoxins. These proteins transfer reducing equivalents to peroxidases, including mitochondrial and cytosolic peroxiredoxins, TcMPx and TcCPx, respectively. In T. cruzi two tryparedoxins have been identified, TXNI and TXNII with different intracellular locations. TXNI is a cytosolic protein while TXNII due to a C-terminal hydrophobic tail is anchored in the outer membrane of the mitochondrion, endoplasmic reticulum and glycosomes. TXNs have been suggested to be involved in a majority of biological processes ranging from redox mechanisms to protein translation. Herein, a comparison of the TXNII interactomes under physiological and oxidative stress conditions was examined. Under physiological conditions, apart from the proteins with unknown biological process annotation, the majority of the identified proteins are related to cell redox homeostasis and biosynthetic processes, while under oxidative stress conditions, are involved in stress response, cell redox homeostasis, arginine biosynthesis and microtubule based process. Interestingly, although TXNII interacts with both peroxiredoxins under physiological conditions, upon oxidative stress, TcMPx interaction prevails. The relevance of the interactions is discussed opening a new perspective of TXNII functions.

Cardiomyocyte oxidants production may signal to T. cruzi intracellular development

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, presents a variable clinical course, varying from asymptomatic to serious debilitating pathologies with cardiac, digestive or cardio-digestive impairment. Previous studies using two clonal T. cruzi populations, Col1.7G2 (T. cruzi I) and JG (T. cruzi II) demonstrated that there was a differential tissue distribution of these parasites during infection in BALB/c mice, with predominance of JG in the heart. To date little is known about the mechanisms that determine this tissue selection. Upon infection, host cells respond producing several factors, such as reactive oxygen species (ROS), cytokines, among others. Herein and in agreement with previous data from the literature we show that JG presents a higher intracellular multiplication rate when compared to Col1.7G2. We also showed that upon infection cardiomyocytes in culture may increase the production of oxidative species and its levels are higher in cultures infected with JG, which expresses lower levels of antioxidant enzymes. Interestingly, inhibition of oxidative stress severely interferes with the intracellular multiplication rate of JG. Additionally, upon H2O2-treatment increase in intracellular Ca2+ and oxidants were observed only in JG epimastigotes. Data presented herein suggests that JG and Col1.7G2 may sense extracellular oxidants in a distinct manner, which would then interfere differently with their intracellular development in cardiomyocytes.

HSP70 of Leishmania amazonensis alters resistance to different stresses and mitochondrial bioenergetics

The 70 kDa heat shock protein (HSP70) is a molecular chaperone that assists the parasite Leishmania in returning to homeostasis after being subjected to different types of stress during its life cycle. In the present study, we evaluated the effects of HSP70 transfection of L. amazonensis promastigotes (pTEX-HSP70) in terms of morphology, resistance, infectivity and mitochondrial bioenergetics. The pTEX-HSP70 promastigotes showed no ultrastructural morphological changes compared to control parasites. Interestingly, the pTEX-HSP70 promastigotes are resistant to heat shock, H2O2-induced oxidative stress and hyperbaric environments. Regarding the bioenergetics parameters, the pTEX-HSP70 parasites had higher respiratory rates and released less H2O2 than the control parasites. Nevertheless, the infectivity capacity of the parasites did not change, as verified by the infection of murine peritoneal macrophages and human macrophages, as well as the infection of BALB/c mice. Together, these results indicate that the overexpression of HSP70 protects L. amazonensis from stress, but does not interfere with its infective capacity.

Trypanosoma cruzi mitochondrial tryparedoxin peroxidase is located throughout the cell and its pull down provides one step towards the understanding of its mechanism of action

Trypanosoma cruzi depends on the effectiveness of redox metabolism to survive and ensure infection in the host. Homeostasis of redox metabolism in T. cruzi is achieved by the actions of several proteins that differ in many aspects from host proteins. Although extensive research has been performed examining hydroperoxide cytosolic antioxidant defense centered on trypanothione, the mechanisms of mitochondrial antioxidant defense are not yet known. The aim of this study was to elucidate the partners of TcMPx antioxidant pathway and to determine the influence of the cellular context (physiological versus oxidative stress). Through co-precipitation coupled with a mass spectrometry approach, a variety of proteins were detected under physiological and oxidative stress conditions. Interestingly, functional category analysis of the proteins identified under physiological conditions showed that they were involved in the stress response, oxidoreduction, thiol transfer, and metabolic processes; this profile is distinct under oxidative stress conditions likely due to structural alterations. Our findings help to elucidate the reactions involving TcMPx and most importantly also reveal that this protein is present throughout the cell and that its interaction partners change following oxidative stress exposure. The involvement and significance of the proteins found to interact with TcMPx and other possible functions for this protein are discussed widening our knowledge regarding T. cruzi mitochondrial antioxidant defenses.

Essential oil from the leaves of Annona vepretorum: chemical composition and bioactivity

The essential oil from the leaves of Annona vepretorun was obtained by hydrodistillation using a Clevenger-type apparatus and analyzed by GC-MS and GC-FID. Eighteen compounds representing 98.1% of the crude essential oil were identified. The major compounds identified were bicyclogermacrene (43.7%), spathulenol (11.4%), alpha-felandrene (10.0%), alpha-pinene (7.1%), (E)-beta-ocimene (6.8%), germacrene D (5.8%), and p-cymene (4.2%). The trypanocidal activity against Trypanosoma cruzi epimastigote forms, as well as, the antimicrobial and antioxidant proprieties was investigated. The essential oil showed a potent trypanocidal activity with IC50 value of 31.9 +/-1.3 microg x mL(-1). For antimicrobial activity, the best result was observed against Candida tropicalis with a MIC value of 100 microg x mL(-1). For antioxidant capacity the essential oil showed weak activity.

Essential Oil from the Leaves of Annona vepretorum: Chemical Composition and Bioactivity

The essential oil from the leaves of Annona vepretorun was obtained by hydrodistillation using a Clevenger-type apparatus and analyzed by GC-MS and GC-FID. Eighteen compounds representing 98.1% of the crude essential oil were identified. The major compounds identified were bicyclogermacrene (43.7%), spathulenol (11.4%), α-felandrene (10.0%), α-pinene (7.1%), (E)-β-ocimene (6.8%), germacrene D (5.8%), and p-cymene (4.2%). The trypanocidal activity against Trypanosoma cruzi epimastigote forms, as well as, the antimicrobial and antioxidant proprieties was investigated. The essential oil showed a potent trypanocidal activity with IC50 value of 31.9±1.3μg.mL-1. For antimicrobial activity, the best result was observed against Candida tropicalis with a MIC value of 100μg.mL-1. For antioxidant capacity the essential oil showed weak activity.

Distinct phosphatase activity profiles in two strains of Trypanosoma cruzi

Phosphorylation of parasite proteins plays a key role in the process of cell invasion by Trypanosoma cruzi, the etiologic agent of Chagas' disease. In this sense, characterization of parasite kinases and phosphatases could open new possibilities for the rational design of chemotherapeutic agents for the treatment of Chagas' disease. In this work, we analyzed phosphatase activities in T. cruzi homogenates from 2 strains belonging to different lineages and with different resistance to oxidative stress. Tulahuen 2 cells (Lineage I) showed higher phosphatase activities and specificity constants when compared to the Y strain (Lineage II). Tulahuen 2 had an optimum phosphatase activity at pH 4.0 and the Y strain at pH 7.0. In both cases, neutral–basic, but not acid, phosphatase activities were increased in the presence of Mg2+. Although calcium had an inhibitory effect at a pH of 7.0 and 8.0 in the Y strain, this inhibition was restricted to pH 8.0 in the other strain. Different substrates and acid phosphotyrosine and alkaline phosphatase inhibitors exhibited distinct effects on the phosphatase activity of both strains. Our results provide a better understanding of T. cruzi phosphatases and reinforce the notion of heterogeneity among T. cruzi populations.

Mechanism of Trypanosoma cruzi death induced by Cratylia mollis seed lectin

Incubation of T. cruzi epimastigotes with the lectin Cramoll 1,4 in Ca(2+) containing medium led to agglutination and inhibition of cell proliferation. The lectin (50 microg/ml) induced plasma membrane permeabilization followed by Ca(2+) influx and mitochondrial Ca(2+) accumulation, a result that resembles the classical effect of digitonin. Cramoll 1,4 stimulated (five-fold) mitochondrial reactive oxygen species (ROS) production, significantly decreased the electrical mitochondrial membrane potential (Delta Psi(m)) and impaired ADP phosphorylation. The rate of uncoupled respiration in epimastigotes was not affected by Cramoll 1,4 plus Ca(2+) treatment, but oligomycin-induced resting respiration was 65% higher in treated cells than in controls. Experiments using T. cruzi mitochondrial fractions showed that, in contrast to digitonin, the lectin significantly decreased Delta Psi(m) by a mechanism sensitive to EGTA. In agreement with the results showing plasma membrane permeabilization and impairment of oxidative phosphorylation by the lectin, fluorescence microscopy experiments using propidium iodide revealed that Cramoll 1,4 induced epimastigotes death by necrosis.

Trypanosoma cruzi strains, Tulahuen 2 and Y, besides the difference in resistance to oxidative stress, display differential glucose-6-phosphate and 6-phosphogluconate dehydrogenases activities

The drugs currently available for Chagas'disease treatment are unsatisfactory due to limited efficacy and toxic side effects, making the search for more specific pharmacological agents a priority. The components of the Trypanosoma cruzi trypanothione-dependent antioxidant system have been pointed out as potential chemotherapeutic targets for the development of more specific drugs. To work properly, this system must have a current supply of NADPH, provided by glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD). Here, we compare two T. cruzi strains, Tulahuen 2 and Y, regarding growth rate, cytosolic tryparedoxin peroxidase (TcCPX) concentration and pentose phosphate pathway dehydrogenases activities. Tulahuen 2 cells show higher values as compared to the Y strain when the following parameters are compared: TcCPX concentration, resistance to H2O2, growth index and G6PD activity. Different patterns of G6PD and 6PGD activities were observed among strains along the growth curve and when cells were challenged with H2O2. These data reinforce the heterogeneity within T. cruzi populations and also the importance of G6PD in protecting the parasite against reactive oxygen species.

Characterization of the intracellular Ca(2+) pools involved in the calcium homeostasis in Herpetomonas sp. promastigotes

Trypanosomatids of the genus Herpetomonas comprises monoxenic parasites of insects that present pro- and opisthomastigotes forms in their life cycles. In this study, we investigated the Ca(2+) transport and the mitochondrial bioenergetic of digitonin-permeabilized Herpetomonas sp. promastigotes. The response of promastigotes mitochondrial membrane potential to ADP, oligomycin, Ca(2+), and antimycin A indicates that these mitochondria behave similarly to vertebrate and Trypanosoma cruzi mitochondria regarding the properties of their electrochemical proton gradient. Ca(2+) transport by permeabilized cells appears to be performed mainly by the mitochondria. Unlike T. cruzi, it was not possible to observe Ca(2+) release from Herpetomonas sp. mitochondria, probably due to the simultaneous Ca(2+) uptake by the endoplasmic reticulum. In addition, a vanadate-sensitive Ca(2+) transport system, attributed to the endoplasmic reticulum, was also detected. Nigericin (1 microM), FCCP (1 microM), or bafilomycin A(1) (5 microM) had no effect on the vanadate-sensitive Ca(2+) transport. These data suggest the absence of a Ca(2+) transport mediated by a Ca(2+)/H(+) antiport. No evidence of a third Ca(2+) compartment with the characteristics of the acidocalcisomes described by A. E. Vercesi et al. (1994, Biochem. J. 304, 227-233) was observed. Thapsigargin and IP(3) were not able to affect the vanadate-sensitive Ca(2+) transport. Ruthenium red was able to inhibit the Ca(2+) uniport of mitochondria, inducing a slow mitochondrial Ca(2+) efflux, compatible with the presence of a Ca(2+)/H(+) antiport. Moreover, this efflux was not stimulated by the addition of NaCl, which suggests the absence of a Ca(2+)/Na(+) antiport in mitochondria.

Peroxynitrite affects Ca2+ transport in Trypanosoma cruzi

Macrophages play an important role against Trypanosoma cruzi infection, via superoxide, nitric oxide, and peroxynitrite production. Peroxynitrite has been shown to be highly cytotoxic against Trypanosoma cruzi epimastigotes. Calcium is involved in many vital functions of the parasites, being its intracellular concentration governed by several transport systems, involving mitochondrial and non-mitochondrial compartments. In this paper, we report the effect of peroxynitrite on the calcium uptake systems, as studied by digitonin-permeabilized trypanosomes in the presence of arsenazo III. Peroxynitrite, at biologically relevant concentrations produced within phagosomes (250-750 microM), inhibited calcium uptake in a dose-dependent manner. Peroxynitrite decreased the mitochondrial membrane potential obtained in the presence of tetramethyl-p-phenylenediamine (TMPD)/ascorbate. In addition, a decrease of the non-mitochondrial Ca(2+)-uptake, concomitant with the inactivation of a Ca(2+)-dependent ATPase activity, was observed. HPLC analyses of the cellular adenine nucleotide pool showed a time-dependent decrease of ATP content and energy charge of the parasite; however this drop in ATP levels was significantly delayed with respect to decrease of the ATP-dependent Ca(2+)-transport. We conclude that the disruption of calcium homeostasis by peroxynitrite may contribute to the observed cytotoxic effects of macrophages against T. cruzi.

Ca2+-independent permeabilization of the inner mitochondrial membrane by peroxynitrite is mediated by membrane protein thiol cross-linking and lipid peroxidation

Peroxynitrite anion, the reaction product of superoxide and nitric oxide, is a potent biological oxidant, which inactivates mammalian heart mitochondrial NADH-coenzyme Q reductase (complex I), succinate dehydrogenase (complex II), and ATPase, without affecting cytochrome c oxidase (complex IV). In this paper, we evaluated the effect of peroxynitrite on mitochondrial membrane integrity and permeability under low calcium concentration. Phosphate buffer was used in most of our experiments since Hepes, Tris, mannitol, and sucrose were found to inhibit the oxidative chemistry of peroxynitrite. Peroxynitrite (0.1-1.0 mM) caused a dose-dependent decrease in the ability of mitochondria to build up a membrane potential when N,N,N',N'-tetramethyl-p-phenylenediamine/ascorbate were used as substrate. Elimination of the membrane potential was accompanied by penetration of the osmotic support (KCl/NaCl) into the matrix as judged by the parallel occurrence of mitochondrial swelling. This swelling was partially inhibited by dithiothreitol (DTT) or butylated hydroxytoluene (BHT) and was insensitive to ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, ADP, and cyclosporin A. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of solubilized membrane proteins indicated that alterations in membrane permeability were associated with the production of protein aggregates due to membrane protein thiol cross-linking. The protective effect of DTT on both mitochondrial swelling and protein polymerization suggests the involvement of disulfide bonds in the membrane permeabilization process. In addition, the increase in thiobarbituric acid-reactive substances and the partial inhibitory effect of BHT indicate the occurrence of lipid peroxidation. These results support the idea that under our experimental conditions peroxynitrite causes mitochondrial structural and functional alterations by Ca2+-independent mechanisms through lipid peroxidation and protein sulfhydryl oxidation.

Disruption of Ca2+ homeostasis in Trypanosoma cruzi by crystal violet

We have demonstrated previously that crystal violet induces a rapid, dose-related collapse of the inner mitochondrial membrane potential of Trypanosoma cruzi epimastigotes. In this work, we show that crystal violet-induced dissipation of the membrane potential was accompanied by an efflux of Ca2+ from the mitochondria. In addition, crystal violet inhibited the ATP-dependent, oligomycin-, and antimycin A-insensitive Ca2+ uptake by digitonin-permeabilized epimastigotes. Crystal violet also induced Ca2+ release from the mitochondria and endoplasmic reticulum of digitonin-permeabilized trypomastigotes. Furthermore, crystal violet inhibited Ca2+ uptake and the (Ca(2+)-Mg2+)-ATPase of a highly enriched plasma membrane fraction of epimastigotes, thus indicating an inhibition of other calcium transport mechanisms of the cells. Disruption of Ca2+ homeostasis by crystal violet may be a key process leading to trypanosome cell injury by this drug.

Evidence for free radical formation during horseradish peroxidase-catalyzed N-demethylation of crystal violet

Crystal violet (gentian violet) can undergo an oxidative metabolism, catalyzed by horseradish peroxidase, resulting in formaldehyde formation. The N-demethylation reaction was strongly inhibited by reduced glutathione. Evidence for the formation of a crystal violet radical during the horseradish peroxidase catalyzed reaction was the detection of thiyl and ascorbate radicals from glutathione and ascorbate, respectively. The concentration of radicals from both compounds was significantly increased in the presence of crystal violet. Oxygen uptake was stimulated when glutathione was present in the system and this oxygen uptake was dependent on the dye and enzyme concentration. Oxygen uptake did not occur when ascorbate, instead of glutathione, was present in the system. However, when glutathione was present, ascorbate totally inhibited the glutathione-stimulated oxygen uptake in the crystal violet/horseradish peroxidase/hydrogen peroxide system. Although a weak ESR spectrum from a crystal violet-derived free radical was detected when the dye reacted with H2O2 and horseradish peroxidase, using the fast flow technique, this spectrum could not be interpreted.

A calmodulin-activated (Ca(2+)-Mg2+)-ATPase is involved in Ca2+ transport by plasma membrane vesicles from Trypanosoma cruzi

High-affinity Ca(2+)-activated ATPases that do not show any demonstrable dependence on Mg2+ have been reported in the plasma membranes of different trypanosomatids, and it has been suggested [McLaughlin (1985) Mol. Biochem. Parasitol. 15, 189-201; Ghosh, Ray, Sarkar & Bhaduri (1990) J. Biol. Chem. 265, 11345-11351] that these enzymes may have a role in Ca2+ transport by the plasma membrane and in the regulation of intracellular Ca2+ in these parasites. In this report we investigated Ca2+ transport by Trypanosoma cruzi plasma membrane vesicles using Arsenazo III as a Ca2+ indicator. These vesicles accumulated Ca2+ upon addition of ATP only when Mg2+ was present and released it in response to the Ca2+ ionophore A23187, but were insensitive to inositol 1,4,5-trisphosphate. Ca2+ transport was insensitive to antimycin A, oligomycin and carbonyl cyanide p-trifluorophenylhydrazone, ruling out any mitochondrial contamination. Staurosporine and phorbol myristate acetate had no effect on this activity, while low concentrations of vanadate (10 microM) completely inhibited it. In addition, we describe a high-affinity vanadate-sensitive (Ca(2+)-Mg2+)-ATPase in the highly enriched plasma membrane fraction of T. cruzi. Kinetic studies indicated that the apparent Km for free Ca2+ was 0.3 microM. On the other hand, Ca(2+)-ATPase activity and Ca2+ transport were both stimulated by bovine brain calmodulin and by endogenous calmodulin purified from these cells. In addition, trifluoperazine and calmidazolium, at concentrations in the range in which they normally exert anti-calmodulin effects, inhibited the calmodulin-stimulated Ca(2+)-ATPase activity. These observations support the notion that a Mg(2+)-dependent plasma membrane Ca2+ pump is present in these parasites.

Digitonin permeabilization does not affect mitochondrial function and allows the determination of the mitochondrial membrane potential of Trypanosoma cruzi in situ

Digitonin can be used to permeabilize selectively the plasma membrane of Trypanosoma cruzi epimastigotes without significantly affecting the functional integrity of mitochondria. Addition of digitonin at concentrations close to 64 microM caused decrease in the rate of basal respiration of epimastigotes similar to that caused by oligomycin. A further addition of carbonyl cyanide p-trifluorophenylhydrazone (FCCP) brought respiration to the same rate observed prior to the inclusion of digitonin or oligomycin. This suggests that like oligomycin, digitonin is shifting respiration to a nonphosphorylating state probably by depleting the cells from adenine nucleotides due to permeabilization of the plasma membrane. The use of low concentrations of digitonin allowed the quantitative determination of the mitochondrial membrane potential of these cells in situ using safranine O. The response of epimastigotes mitochondrial membrane potential to phosphate, FCCP, valinomycin, nigericin, ADP, and Ca2+ indicates that these mitochondria behave similarly to vertebrate mitochondria regarding the properties of their electrochemical proton gradient. In addition, T. cruzi mitochondria are able to build up and retain a membrane potential of a value comparable to that of mammalian mitochondria. The trypanocidal drug crystal violet, as well as other cationic drugs such as dequalinium, induced a rapid dose-related collapse of the inner mitochondrial membrane potential.

Ca2+ transport in digitonin-permeabilized trypanosomatids

The use of digitonin to permeabilize Leishmania mexicana mexicana, Leishmania agamae, and Crithidia fasciculata plasma membranes enabled us to study Ca2+ transport in situ. The present results show that the mitochondria of these trypanosomatids are able to build up and retain a membrane potential as indicated by a tetraphenylphosphonium-sensitive electrode. Ca2+ uptake caused membrane depolarization compatible with the existence of an electrogenically mediated Ca2+ transport mechanism in these mitochondria. Ca2+ uptake was partially inhibited by ruthenium red, almost totally inhibited by carbonyl cyanide p-trifluoromethoxyphenylhydrazone, and stimulated by inorganic phosphate. Large amounts of Ca2+ were retained by C. fasciculata mitochondria even after addition of thiols and NAD(P)H oxidants such as t-butylhydroperoxide and diamide. In contrast, Ca2+ was not retained in the matrix of Leishmania sp. mitochondria for long periods of time. In addition to the mitochondrial Ca2+ uptake, a vanadate-sensitive Ca2(+)-transporting system was also detectable in these trypanosomatids.

The mitochondrion of Trypanosoma cruzi is a target of crystal violet toxicity

The first morphological alteration observed in Trypanosoma cruzi different stages upon incubation with crystal violet was mitochondrial swelling. The use of digitonin to solubilize T. cruzi plasma membrane allowed the demonstration of an uncoupling action of crystal violet on epimastigote mitochondria in situ. Low concentrations of crystal violet (20-50 microM) or carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP; 0.5 microM) uncoupled the respiratory control mechanism. The inhibition of State 3 respiration by oligomycin was released by crystal violet or FFCCP. Crystal violet released respiratory control, and enhanced ATPase activity of digitonin-permeabilized epimastigotes. Higher concentrations of crystal violet inhibited mitochondrial respiration. The uncoupled effect of crystal violet was stimulated by inorganic phosphate. In addition, crystal violet inhibited endongenous and glucose-stimulated respiration of the intact epimastigotes, and inhibited the Mg2+-ATPase in the epimastigote mitochondrial fractions. The inhibition of this Mg2+-ATPase increased up to pH 9.0 and decreased with increasing protein concentration. These data indicate that the T. cruzi mitochondrion is apparently the main target of crystal violet toxicity.

Crystal violet as an uncoupler of oxidative phosphorylation in rat liver mitochondria

Crystal violet exhibited characteristics of an uncoupler of oxidative phosphorylation, i.e. it released respiratory control, hindered ATP synthesis, enhanced ATPase activity, and produced swelling of isolated rat liver mitochondria. Maximal stimulation of respiration, ATPase activity, and swelling was observed at a concentration of 40 microM. The inhibition of State 3 respiration by oligomycin was released by crystal violet. High concentrations of crystal violet inhibited mitochondrial respiration. The uncoupling effect of crystal violet required inorganic phosphate and was abolished by N-ethylmaleimide. The adenine nucleotides ADP and ATP protected mitochondria from uncoupling by the dye. The dye taken up by mitochondria was released into the incubation medium on induction of uncoupling. In the absence of phosphate, the dye did not cause uncoupling, but its retention was much greater than in the presence of phosphate. Crystal violet is suggested to induce uncoupling by acting on the membrane, rather than by its electrophoretic transfer into the mitochondria.