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P Azambuja

Publications and source records attributed to P Azambuja.

At least 19 recordsLinked to original sources
PubMed1999

Studies on a haemolymph lectin isolated from Rhodnius prolixus and its interaction with Trypanosoma rangeli.

We demonstrated that in Rhodnius prolixus haemocyte monolayers, both Trypanosoma cruzi and Trypanosoma rangeli are capable of inducing haemocyte/parasite clump formation. We also purified, by one-step affinity chromatography, a haemolymph galactoside-binding lectin from R. prolixus which we believe could play an important role in the development of T. rangeli in the haemocoel of the insect vector. This lectin markedly enhanced the activation of clump formation by T. rangeli in R. prolixus haemocyte monolayers, with an increase in clump size and haemocyte aggregation. The haemolymph lectin also significantly affected the motilitity and survival of T. rangeli culture short forms, but not the long forms, when they were incubated in vitro. This molecule is also one of the few described in insects with agglutination activity independent of calcium ions. The partial N-terminal amino acid sequence of this lectin demonstrated similarity to a bacterial xylulose kinase and in preliminary experiments the purified haemolymph lectin phosphorylated a tyrosine kinase substrate in a dose-dependent manner. The possible role of this haemolymph lectin in the life cycle of T. rangeli is discussed.

Amino Acid Sequence↗
PubMed1999

Influence of brain and azadirachtin on Trypanosoma cruzi development in the vector, Rhodnius prolixus.

Studies on the effects of decapitation, head transplantation, azadirachtin, and ecdysone therapy on the ultrastructural organization of the midgut of Rhodnius prolixus, a vector of the protozoan Trypanosoma cruzi, show a distinct effect on the organization of the epithelial cells. When insects are decapitated or treated with azadirachtin, the ultrastructural organiza tion of these compartments changed significantly and drastically blocked the development of T. cruzi infection. In converse experiments, head transplantation or oral therapy with ecdysone significantly re versed the T. cruzi infectivity and reestablished the organization of the stomach and intestine in decapitated or azadirachtin-treated insects. These results indicat that a brain factor, possibly the prothoracicotropic hormone which stimulates ecdysteroid production on the prothoracic glands, may act directly or indirectly on both the midgut cell organiza tion and the intestinal microenvironment, interfering in the trypanosome survival and infection of the vector R. prolixus.

Animals↗
PubMed1999

Rhodnius prolixus infected with Trypanosoma rangeli: In vivo and in vitro experiments.

Studies were carried out on the activation of the prophenoloxidase (proPO) in adults of Rhodnius prolixus infected by short and long epimastigote forms of Trypanosoma rangeli. The in vitro activation of the proPO cascade using l-DOPA as substrate was very low in the absence of fat body extract, hemolymph, and parasites. On the other hand, a higher PO activity was observed when short, but not long, epimastigotes of T. rangeli were incubated with fresh hemolymph, fat body extract, and l-DOPA. Supernatant from lysed long epimastigotes increased the PO activity at levels identical to those observed with supernatants from lysed short epimastigotes. Similarly, the PO activity of hemolymph obtained from inoculated insects with long epimastigotes of T. rangeli showed a very low activity when incubated with l-DOPA compared to the PO activity of hemolymph taken from insects inoculated with short epimastigotes of T. rangeli. Control insects inoculated with sterile PBS showed no PO activity. These data indicate the presence of (a) factor(s) in the hemolymph as well as in the fat body extract that may be released (or induced) by the presence of short epimastigotes of T. rangeli and which results in the activation of the R. prolixus proPO system. The implications of these findings are discussed in relation to the development of T. rangeli and its ability to overcome the proPO system, survive, and successfully colonize the hemolymph of R. prolixus.

Animals↗
PubMed1999

Neolignans inhibit Trypanosoma cruzi infection of its triatomine insect vector, Rhodnius prolixus.

Two neolignans, burchellin and nordihydroguaiaretic acid (NDGA), were toxic only to Trypanosoma cruzi clone Dm28c maintained in brain heart infusion (BHI) medium at a concentration of 100 microg/ml, not 10 microg/ml. When Rhodnius prolixus was fed with epimastigotes of T. cruzi and treated simultaneously with a single dose of burchellin or NDGA at 10 pg/ml of blood meal the number of parasites in the gut decreased. Whereas burchellin was only partially active, NDGA drastically reduced the number of epimastigotes and metacyclic trypomastigotes of T. cruzi in the excreta (urine plus feces). When the insect larvae were pretreated with burchellin or NDGA at 20 days before the infection with T. cruzi a significant reduction in the number of parasites in the gut occurred. However, when both compounds were applied at 20 days after the establishment of T. cruzi infection, although burchellin significantly reduced the gut infection, neither compound could abolish the infection entirely within the subsequent 15 days.

Animals↗
PubMed1997

Biological effects of canatoxin in different insect models: evidence for a proteolytic activation of the toxin by insect cathepsinlike enzymes.

Canatoxin is a toxic protein isolated from the jackbean, Canavalia ensiformis. The toxin injected intraperitoneally is lethal for mice and rats; however, it is inactive if given orally. In this study, Manduca sexta (L.) (Lepidoptera), Schistocerca americana (Drury) (Orthoptera), Drosophila melanogaster (L.) (Diptera), Aedes aegypti (L.) (Diptera), Rhodnius prolixus (Stål) (Hemiptera), and Callosobruchus maculatus (F.) (Coleoptera) were fed on canatoxin-containing diets. No effects were seen in M. sexta, S. americana, D. melanogaster, or A. aegypti. No traces of canatoxin were found in their feces, suggesting that the protein was digested completely by these insects, which characteristically have a trypsin-based digestion. In contrast, canatoxin was lethal for insects displaying cathepsin-based digestion. Thus, for C. maculatus, a diet containing 0.25% wt:wt canatoxin caused complete inhibition of larval growth. When R. prolixus were fed on canatoxin, 2 effects were seen: impairment of water excretion and increased lethality 48-96 h after feeding. The lethal effect of canatoxin in R. prolixus was blocked partially or completely when the digestion of the toxin by R. prolixus midgut enzymes was impaired. The data showed that canatoxin is highly toxic when ingested by some species of insects but not affecting others, probably in correlation with the characteristics of the digestive process of the insect.

Aedes↗
PubMed1996

Differential in vitro and in vivo behavior of three strains of Trypanosoma cruzi in the gut and hemolymph of Rhodnius prolixus.

A comparison was made of the agglutination and lysis of three strains of Trypanosoma cruzi in gut extracts and hemolymph of Rhodnius prolixus and the results obtained were correlated with the success or failure of the parasite strain to infect the digestive tube or to survive in the hemocel after inoculation. Both T. cruzi strains Dm28c and Cl urine 35 days after feeding with parasites. Concomitantly, both of these strains were agglutinated but not lysed by the crop extracts. In contrast, T. cruzi Y strain parasites rapidly disappeared from the gut and showed no agglutination, but some lysis, in the crop extract. Following inoculation into the hemocel, only the Cl strain survived at high levels and was also the only strain agglutinated significantly in the hemolymph. Both Dm28c and Y strains rapidly disappeared from the hemocel with the former parasite being removed more slowly than the latter, probably due to clearance by the cellular defenses. The rapid clearance of the Y strain was correlated with the presence of a high titer lysin in the hemolymph. Subsequent experiments using FITC-labeled lectins and FACS to probe the carbohydrates on the parasite surfaces showed significant differences between the three strains. Thus, only Dm28c was stained strongly by Arachis hypogea (PNA) lectin, indicating the presence of galactose/N-acetylgalactosamine residues, and Dm28c and Y strains by Phytolacca lectin for N-acetyl glucosamine moieties. Finally, the fact that, in contrast to Dm28c and Y, the Cl strain strongly interacted with Triticum vulgaris (WGA) but not with Phytolacca lectin may be due to the presence of N-acetyl neuraminic acid residues on these organisms. These surface carbohydrate differences may be correlated both to the behavior and agglutination variations between the three strains recorded in this work.

Agglutination Tests↗
PubMed1996

Trypanosoma cruzi and erythrocyte agglutinins: a comparative study of occurrence and properties in the gut and hemolymph of Rhodnius prolixus.

The activity of agglutinins found in the gut tissues and hemolymph of Rhodnius prolixus was tested using rabbit erythrocytes, Trypanosoma cruzi, or Trypanosoma rangeli as test particles. In addition, investigations were made of the influence of parasitic infection and insect diet on the agglutination titers. A range of physicochemical tests and carbohydrate-binding studies were performed and inhibitors were subsequently found for both the crop agglutinin (p-nitrophenol-derived sugars) and the hemolymph agglutinin (galactose-type sugars). As a result, affinity chromatography was utilized for an attempted purification of these agglutinins, and a one-step purification protocol for the R. prolixus hemolymph agglutinin has been developed. Preliminary results of some biological and physicochemical characteristics of this pure agglutinin are described. These results represent a starting point for future studies of lectin/parasite interaction in this reduviid-trypanosome model.

Animals↗
PubMed1995

Trypanosoma cruzi and Trypanosoma rangeli: interplay with hemolymph components of Rhodnius prolixus.

Studies were carried out on the course of infection of Trypanosoma cruzi (clone Dm28c) and Trypanosoma rangeli (clone San Agustin) and their interactions with hemolymph components of Rhodnius prolixus. These parasites when inoculated into the hemocoel of adult R. prolixus (i) had different courses of infection (T. rangeli had high rates of both multiplication and infection and T. cruzi had no division and disappeared soon from the hemolymph); (ii) induced high but no differential increases in lysozyme levels; (iii) failed to induce any other antibacterial activity; (iv) showed similar patterns of hemolymph agglutination activity for erythrocytes and parasites, although there was evidence of limited, unquantifiable, agglutination of T. cruzi; (v) elicited different hemocyte responses with only the T. rangeli infection resulting in significantly increased hemocyte counts; and (vi) did not induce trypanolytic activity. These experiments, unlike previous studies, also showed (i) an interaction of these trypanosomes with the prophenoloxidase-activating system [phenoloxidase (PO) production was spontaneously activated by both parasites but the number of T. cruzi in the hemolymph was directly correlated with PO levels] and (ii) that the elimination of T. cruzi also corresponded to the formation of nodules in the hemolymph. The significance of these results is discussed in relation to the hypothesis that T. rangeli but not T. cruzi has the ability to escape from and perhaps utilize the vector immune system in order to successfully colonize the R. prolixus hemolymph.

Animals↗
PubMed1994

Rhodnius prolixus: salivary antihemostatic components decrease with Trypanosoma rangeli infection.

Feeding behavior and some antihemostatic properties of the saliva of Rhodnius prolixus infected with Trypanosoma rangeli were studied and compared with those of uninfected controls. Insects with salivary gland infection pierced host skin more often and drew less blood and at a lower rate than controls when feeding on a rabbit. None of these differences was observed when feeding was performed through a membrane feeder. Salivary gland homogenates from infected insects, at 30 days after feeding/infection, had a significantly lower amount of total protein/salivary gland pair and less anticoagulant activity than controls. Also, infected salivary glands exhibited significantly reduced apyrase activities and reactive nitrogen groups when compared to controls. It is concluded that salivary infection of T. rangeli impairs the ability of the vector to locate blood vessels by affecting salivary antihemostatic properties, thus enhancing the possibility of intradermal inoculation of parasites into the mammalian host.

Animals↗
PubMed1991

Effects of azadirachtin in Rhodnius prolixus: data and hypotheses.

The effects of azadirachtin A, a tetranortriterpenoid from the neem tree Azadirachta indica J., on both development and interaction between Trypanosoma cruzi, the causative agent of Chagas' disease, and its vector Rhodnius prolixus were studied. Given through a blood meal, a dose-response relationship of azadirachtin was established using antifeedant effect and ecdysis inhibition as effective parameters. A single dose of azadirachtin A was able to block the onset of mitosis in the epidermis and ecdysteroid titers in the hemolymph, determined by radioimmuneassay, were too low for an induction of ecdysis. The survival of T. cruzi was also studied in R. prolixus treated with the drug. If the trypomastigotes were fed in presence of azadirachtin A the number of parasites drastically decreased. If the drug was applied after infection of the bug with T. cruzi, the parasite was still abolished from the gut. If the insect was pretreated with azadirachtin A before infection the same observation was obtained. A single dose of azadirachtin A was enough for a permanent resistance of the insect host against its reinfection with T. cruzi and for blocking the ecdysis for a long time. The effects of azadirachtin A on the hormonal balance of the host and growth inhibition of the parasite will be discussed on the basis of the present results.

Animals↗
PubMed1989

In vitro cytotoxicity of Rhodnius prolixus hemolytic factor and mellitin towards different trypanosomatids.

Trypanosoma cruzi strain Y and clone Dm28c and other trypanosomatids were exposed to two lytic agents, Rhodnius prolixus hemolytic factor (RHF) and mellitin, in vitro. In both cases, the result was a significant decrease in the number of parasites after a 30-min treatment at 37 degrees C. RHF and mellitin had distinct activities on different strains and species of trypanosomatids. These observations suggest that RHF may be an important factor in selecting resistant strains of trypanosomes for development in the vector's gut.

Animals↗
PubMed1987

Demonstration of a proallatotoxin-sensitive period in 4th-instar nymphs of Rhodnius prolixus.

1. Topical application of the proallatotoxin ethoxyprecocene II (60 micrograms/nymph) to 4th-instar nymphs of Rhodnius prolixus at various times before and after a blood meal induced precocious metamorphosis. 2. The highest percentage of adultoids was obtained when proallatotoxin was applied prior to feeding or up to day 3 after the blood meal. 3. The proallatotoxin-sensitive period ended 4 days after feeding just before the maximum peak of ecdysteroid concentration in the hemolymph. 4. The significance of these findings is discussed in terms of the juvenile hormone-sensitive period and the hormonal program which controls molting in this insect.

Administration, Topical↗
PubMed1987

Characterization of inducible lysozyme activity in the hemolymph of Rhodnius prolixus.

1. The characterization and partial purification of an induced lysozyme activity in the hemolymph of adult Rhodnius prolixus inoculated with Micrococcus lysodeikticus is described. 2. Little or no activity against M. lysodeikticus appeared in the first hours after inoculation, but the activity increased reaching a maximum 4 days later, which was maintained to day 12. 3. The activity was characterized as lysozyme on the basis of the following considerations: 1) pH optimum and thermostability at acidic pH; 2) rate of lysis negatively dependent on ionic strength; 3) binding to SP-Sephadex at pH 5.5; 4) apparent molecular weight of 15 kDal. 4. Crude or semi-purified enzyme preparations showed a high degree of stability during handling, freezing and thawing, and standing at 5 degrees C. 5. Incubation of abdominal fat bodies from treated insects resulted in the release of activity into the medium. 6. The relationship between induced lysozyme activity and its role as an insect defense mechanism is discussed.

Animals↗
PubMed1985

A protein diet initiates oogenesis in Rhodnius prolixus.

Oogenesis in R. prolixus females is induced by feeding blood, blood plasma, a suspension of washed erythrocytes, or 5% solutions of egg albumin, bovine serum albumin or hemoglobin. Unfed females and those fed saline, casein hydrolysate, dextran or sucrose do not initiate oogenesis. The juvenile hormone analogue epoxygeranylgeraniol methyl ester induced oogenesis in unfed females as well as in ethoxyprecocene II-treated insects. The results show that a protein meal was sufficient to initiate oogenesis. They also support the view that oogenesis depends on a relationship between protein ingestion and corpus allatum function and that oogenesis is not controlled by hormones released in response to abdominal stretching.

Animals↗
PubMedDate not supplied

Chagas' disease and its insect vector. Effect of azadirachtin A on the interaction of a triatomine host (Rhodnius prolixus) and its parasite (Trypanosoma cruzi).

The ED50 for moulting inhibition by injected azadirachtin A is for fourth instar larvae of all the triatomines, Triatoma vitticepes, T. pseudomaculata, T. maculata, T. brasiliensis, T. lecticularis, T. matogrossensis, T. infestans, Rhodnius prolixus. R. neglectus, R. robustus, Panstrongylus megistus, and P. herrera in the range of 10-25 ng/larva. In Rhodnius prolixus, the survival of T. cruzi was studied after treatment with the drug. If the trypomastigotes were fed in presence of 1.0 microgram azadirachtin A/ml blood, the number of parasites decreased near to the limit of detection within 30 days. If the drug was applied 20 days after T. cruzi infection, it still completely abolished the parasite in the host's gut within the subsequent 20 days. The same holds true if the insect larvae were pretreated with azadirachtin A 20 days before the subsequent infection with T. cruzi. Azadirachtin A. if applied at the dose of 1 microgram/ml, did not affect the hemolytic activity of the crop contents or the proteinase content of the intestine. A parallel between azadirachtin effects on the hormone balance of the host and growth inhibition of the parasite is discussed on the basis of the present results.

Animals↗