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Biomedical subjects

P Azambuja

Publications and source records attributed to P Azambuja.

At least 19 recordsLinked to original sources
PubMed2006

Antiserum against perimicrovillar membranes and midgut tissue reduces the development of Trypanosoma cruzi in the insect vector, Rhodnius prolixus.

Antiserum raised against Rhodnius prolixus perimicrovillar membranes (PMM) and midgut tissue interfered with the midgut structural organization and reduced the development of Trypanosoma cruzi in the R. prolixus insect vector. SDS-PAGE and Western blot analyses confirmed the specific recognition of midgut proteins by the antibody. Feeding, mortality, molt, and oviposition of the insects were unaffected by feeding with the antiserum. However, the eclosion of the eggs were reduced from R. prolixus females treated with antiserum. Additionally, in vivo evaluation showed that after oral treatment with the antiserum, the intensity of infection with the Dm-28c clone of T. cruzi decreased in the digestive tract of fifth-instar nymphs and in the excretions of R. prolixus adults. These results suggest that the changes observed in the PMM organization in the posterior midgut of R. prolixus may not be important for triatomine survival but the antiserum acts as a transmission-reduction vaccine able to induce significant decreases in T. cruzi infection in the vector.

Animals↗
PubMed2005

Effect of blood components, abdominal distension, and ecdysone therapy on the ultrastructural organization of posterior midgut epithelial cells and perimicrovillar membranes in Rhodnius prolixus.

The effects of blood components, nerve-cord severance, and ecdysone therapy on the posterior midgut epithelial cells of 5th-instar Rhodnius prolixus nymphs 10 days after feeding were analyzed by transmission electron microscopy. Cutting the nerve-cord of the blood-fed insects partially reduced the development of microvilli and perimicrovillar membranes (PMM), and produced large vacuoles and small electrondense granules; insects fed on Ringer's saline diet exhibited well developed microvilli and low PMM production; swolled rough endoplasmatic reticulum and electrondense granules; Ringer's saline meal with ecdysone led to PMM development, glycogen particles, and several mitochondria in the cytoplasm; epithelial cells of the insects fed on Ringer's saline meal whose nerve-cord was severed showed heterogeneously distributed microvilli with reduced PMM production and a great quantity of mitochondria and glycogen in the cytoplasm; well developed microvilli and PMM were observed in nerve-cord severed insects fed on Ringer's saline meal with ecdysone; Ringer's saline diet containing hemoglobin recovered the release of PMM; and insects fed on human plasma showed slightly reduced PMM production, although the addition of ecdysone in the plasma led to a normal midgut ultrastructural organization. We suggest that the full development of microvilli and PMM in the epithelial cells depends on the abdominal distension in addition to ingestion of hemoglobin, and the release of ecdysone.

Animals↗
PubMed2004

Lignoids in insects: chemical probes for the study of ecdysis, excretion and Trypanosoma cruzi-triatomine interactions.

The effects of phytochemicals (lignans and neolignans) are reviewed in a variety of insect species with special focus on the recent advances on feeding, excretion and Trypanosoma cruzi interactions with Rhodnius prolixus. Burchellin, podophyllotoxin, pinoresinol, sesamin, licarin A, and nordihydroguaiaretic acid (NDGA) added to the diet of Rhodnius prolixus larvae induce antifeedant effects only in doses up to 100 microg/ml of blood meal. Additionally, pinoresinol and NDGA significantly inhibit ecdysis (ED(50)<20 microg/ml). Simultaneous application of ecdysone (1 microg/ml) counteracts ecdysial stasis as induced by NDGA in 5th-instar larvae. Experiments in vivo demonstrate that burchellin and podophyllotoxin (100 microg/ml) diminish excretion post-feeding. Simultaneous treatment with 5-hydroxytryptamine (1 mM, 5-HT), a diuretic hormone, partially reverses this effect of burchellin. Experiments in vitro, using isolated Malpighian tubules of R. prolixus, indicate that burchellin (i) decreases diuretic hormone levels in the hemolymph but not the amount of diuretic hormone stored in the thoracic ganglionic masses (including axons); (ii) reduces the volume of urine secreted by isolated Malpighian tubules; and (iii) 5-HT therapy cannot overcome the effect of burchellin on the Malpighian tubules. In R. prolixus fed on blood containing T. cruzi epimastigotes, the number of parasites in the digestive tract decreases drastically in the presence of burchellin and NDGA (10 microg/ml). When these phytochemicals are applied 20 days after T. cruzi infection, burchellin significantly reduces the gut infection, whereas NDGA does not. However, if the insects are pretreated with both compounds 20 days before subsequent infection with epimastigotes, the parasite infection is almost completely abolished. The same holds true when 5th-instar of R. prolixus are inoculated with 0.5 microg/microl/larva of both neolignans 1 day before infection. Taken together, these findings not only provide a better understanding of the lignoid function in insects, but also offer novel insights into basic physiological processes, which make lignoids interesting candidates for new types of insecticides.

Animals↗
PubMed2003

Suppression of the prophenoloxidase system in Rhodnius prolixus orally infected with Trypanosoma rangeli.

Investigations were carried out to compare aspects of the prophenoloxidase (proPO)-activating pathway in Rhodnius prolixus hemolymph in response to oral infection and inoculation of the insects with two developmental forms of Trypanosoma rangeli epimastigotes strain H14. In vivo experiments demonstrated that in control insects fed on uninfected blood, inoculation challenge with short epimastigotes resulted in high phenoloxidase (PO) activity. In contrast, previous feeding on blood containing either short or long epimastigotes was able to suppress the proPO activation induced by thoracic inoculation of the short forms. In vitro assays in the presence of short epimastigotes demonstrated that control hemolymph or hemolymph provided by insects previously fed on blood containing epimastigotes incubated with fat body homogenates from control insects significantly increased the PO activity. However, fat body homogenates from insects previously fed on blood containing epimastigotes, incubated with hemolymph taken from insects fed on control blood or blood infected with epimastigotes, drastically reduced the proPO activation. The proteolytic activity in the fat body homogenates of control insects was significantly higher than in those obtained from fat body extracts of insects previously fed on blood containing epimastigotes. These findings indicate that the reduction of the proteolytic activities in the fat body from insects fed on infected blood no longer allows a significant response of the proPO system against parasite challenge. It also provides a better understanding of T. rangeli infection in the vector and offer novel insights into basic immune processes in their invertebrate hosts.

Animals↗
PubMed2002

Dynamic development of Trypanosoma cruzi in Rhodnius prolixus: role of decapitation and ecdysone therapy.

Decapitation and ecdysone therapy on the population dynamics of the Trypanosoma cruzi Dm28c clone in the stomach, small intestine and rectum of fifth-instar larvae of Rhodnius prolixus were investigated. Parasites were not found in the small intestine and rectum of decapitated insects after 10 days post-infection (p.i.). Decapitated ecdysone-supplemented insects sustained the flagellate infection in both gut compartments. In the rectum, the population density of parasites increased 5-fold in ecdysone-treated decapitated larvae and 7-fold in control insects. Epimastigote forms dominated with 40-65%, intermediate stages and round forms varied over 10-35% in the stomach, small intestine and rectum in both insect groups. Low numbers of metacyclic trypomastigotes were observed in the stomach and small intestine of the control group and decapitated insects supplemented with ecdysone but, at 15 days p.i., this form of flagellate reached about 20% in the rectum of the control insects. In the entire gut, at 30 days p.i., 23% of parasites in the control group and 8% in the decapitated insects treated with ecdysone were found. These results indicate that a head factor, possibly the prothoracicotropic hormone from the brain which stimulates ecdysone production by the prothoracic glands, may act directly or indirectly to stimulate the development of epimastigotes and round forms of the parasite and that a single ecdysone treatment is not able to fully reverse metacyclogenesis in decapitated R. prolixus.

Animals↗
PubMed2002

Effects of gamma irradiation on the development of Trypanosoma rangeli in the vector Rhodnius prolixus.

Studies on the effects of gamma radiation on the infectivity of Trypanosoma rangeli (strain H14) for the vector Rhodnius prolixus revealed that (i) the LD(50) (lethal dose for 50% of bugs) for uninfected insects was 4147 rads; (ii) irradiated insects with a dose of 1200 rads subsequently infected with the flagellates exhibited a mortality of 45%, while uninfected irradiated insects showed a mortality of 5%, and infected nonirradiated insects exhibited 10% mortality; (iii) flagellates were present in the hemolymph of irradiated insects 7 days postinfection (p.i.), while in nonirradiated insects the parasites appeared in the hemocoel 18 days p.i.; (iv) T. rangeli infection decreased the number of hemocytes significantly and induced the formation of nodules in the hemolymph of both irradiated and nonirradiated insects; and (v) gamma irradiation affected the ultrastructural organization of the epithelial cells of the small intestine, principally the perimicrovillar membranes and microvilli. In this paper, we discuss the significance of the intestinal microenvironment of R. prolixus with regard to its interaction with T. rangeli.

Animals↗
PubMed2001

Role of superoxide and reactive nitrogen intermediates in Rhodnius prolixus (Reduviidae)/Trypanosoma rangeli interactions.

This study compares aspects of the superoxide, nitric oxide and prophenoloxidase pathways in Rhodnius prolixus hemolymph, measured in parallel, in response to Trypanosoma rangeli inoculation. Responses to two strains of T. rangeli, and two developmental forms, were studied, and the results obtained were correlated with the ability of the parasites to survive, multiply, and complete their life cycles in the hemolymph of the host. T. rangeli H14 strain parasites, which fail to complete their life cycle in Rhodnius by invading the salivary glands, stimulated high levels of superoxide and prophenoloxidase activity, which peaked 24 h after inoculation. Simultaneously, the concentration of hemolymph nitrites and nitrates increased, indicative of nitric oxide activity, but parasite numbers remained low. T. rangeli Choachi strain parasite inoculation also stimulated superoxide and prophenoloxidase activity, which, though significantly lower than the equivalent responses to the H14 strain, also peaked at 24 h. However, nitrate and nitrite levels in Choachi strain-inoculated hemolymph remained low, and this parasite strain multiplied rapidly, especially following peak superoxide activity, and eventually invaded the salivary glands for transmission to a vertebrate host. In both strains, short form epimastigotes stimulated greater superoxide and prophenoloxidase responses than long form epimastigotes. Injection of the NADPH oxidase inhibitor N-ethylmaleimide or the inducible nitric oxide synthase inhibitor S-methyl isothiourea sulfate caused significantly higher insect mortalities in groups of R. prolixus inoculated with either parasite strain compared with those of uninfected control insects. This indicates that both NADPH oxidase and nitric oxide synthase activity may be involved in the immune response of R. prolixus to infection by T. rangeli. Finally, Western blotting of R. prolixus hemocyte lysates revealed the presence of a protein immunologically related to the human NADPH oxidase complex, the initiator enzyme of the respiratory burst.

Animals↗
PubMed2001

Burchellin: effects on Triatoma infestans and on Trypanosoma cruzi within this vector.

Supplementation of blood with the neolignan burchellin (50 microg/ml), a compound from the arboreous Lauraceae Aniba burchelli, affected the ingestion of blood and the course of excretion of fourth- and fifth-instar larvae of Triatoma infestans, the latter especially within the first 4 h after feeding. The total resultant weight loss of treated fourth instars within 24 and 48 h after feeding was only 24% and 28% vs 41% and 48%, respectively, in untreated bugs. In fifth instars, the total weight losses of untreated bugs within 24 and 48 h after feeding were 38% and 41% whereas the weight of treated bugs decreased by 28% and 34%, respectively. In a treatment of Trypanosoma cruzi-infected fourth instars, burchellin significantly reduced the population density of the established infection in the rectum at 5 and 10 days after feeding. This was especially due to a significant increase in the number of the main dividing stage, the epimastigote.

Animals↗
PubMed2000

Rhodnius prolixus: effects of the neolignan burchellin on in vivo and in vitro diuresis.

Supplementation of blood with the neolignan burchellin (100 microg/ml), a compound from the arboreous Lauraceae Aniba burchelli, affected the course of excretion of fourth-instar larvae of Rhodnius prolixus, especially directly after feeding, and reduced the volume of feces/urine excreted within 6 h of feeding to about 18% and, on the simultaneous addition of the diuretic hormone analogue 5-hydroxytryptamine (5-HT), about 71% of that observed in untreated bugs. In the latter, 5-HT induced a significant 60% increase in excretion. Regardless of whether Malpighian tubules originating from unfed, untreated or fed, burchellin-treated bugs were incubated in vitro in the hemolymph of these bugs or in physiological saline supplemented with 5-HT with or without burchellin or in homogenates of thoracic ganglionic masses of untreated and treated bugs, burchellin was consistently found to affect the secretion rates. Therefore, burchellin not only depresses the release of the diuretic hormone or induces the release of antidiuretic factors but also directly affects the Malpighian tubules.

Animals↗
PubMed2000

Effects of lignoids on a hematophagous bug, Rhodnius prolixus: feeding, ecdysis and diuresis.

The effects of lignoids on feeding, ecdysis and diuresis in fourth-instar larvae of Rhodnius prolixus (Hemiptera) were investigated. Up to 100 microg/ml burchellin, podophyllotoxin, pinoresinol, sesamin, licarin A, or nordihydroguaiaretic acid (NDGA) in the diet did not induce antifeedant effects. Pinoresinol and NDGA significantly inhibited ecdysis. In experiments in vivo, burchellin and podophyllotoxin reduced the production of urine after feeding. 5-Hydroxytryptamine (5-HT), a diuretic hormone, partially counteracted this effect of burchellin. In experiments in vitro, using isolated Malpighian tubules, (i) burchellin reduced diuretic hormone levels in the hemolymph but not the amount of diuretic hormone stored in the thoracic ganglionic masses (including axons), (ii) burchellin decreased the volume of urine secreted by isolated Malpighian tubules, and (iii) 5-HT could not overcome the effect of burchellin upon the Malpighian tubules. We conclude that burchellin interfered with the release, but not with the production of diuretic hormone by the thoracic ganglionic mass or induced an antidiuretic hormone and directly affected the Malpighian tubules.

Animals↗
PubMed2000

Effects of some lignans and neolignans on the development and excretion of Rhodnius prolixus.

The effects of six lignans and neolignans as inhibitors of ecdysis and on the water balance in fourth-instar larvae of Rhodnius prolixus were studied by oral, topical and continuous contact treatments. The main results may be summarised as follows: (i) burchellin, pinoresinol, sesamin, licarin A and nordihydroguaiaretic acid (NDGA) did not cause feeding inhibition at doses of 100 micrograms/ml blood; podophyllotoxin had no antifeedant effect but caused a high moulting inhibition and significant toxicity when applied either orally or topically; (ii) the highest ecdysis inhibitory effects were observed with pinoresinol and NDGA when applied orally at a dose of 100 micrograms/ml (58% and 50% of moulting inhibition, respectively); burchellin inhibited 30% of the moulting at this concentration; (iii) by topical treatment none of the compounds presented any influence on the moulting cycle; and (iv) podophyllotoxin and burchellin significantly reduced the excretion of the insect in 24 h; the other compounds had no effect on excretion. The implications of these findings in relation to the pertinent biological events in R. prolixus are discussed.

Animals↗
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↗
PubMed1998

Role of the head in the ultrastructural midgut organization in Rhodnius prolixus larvae: evidence from head transplantation experiments and ecdysone therapy.

Studies on the effects of decapitation, head transplantation and ecdysone therapy on the ultrastructural organization of the midgut in 5th-instar larvae of Rhodnius prolixus, were carried out. Control insects had a typical and significant organization of the epithelial cells (mainly microvilli, extracellular membrane layers and basal portion of the epithelial cells) of the midgut (stomach and intestine) during the entire period of the experiment. However, the host larvae, when decapitated 1 day after feeding, demonstrated significant changes in the ultrastructural organization of the epithelial cells of these compartments. In converse experiments, head transplantations from untreated donors 4-5 days after feeding into headless larvae sustained the ultrastructural organization of the epithelial cells in the midgut. Oral therapy with ecdysone (5 &mgr;g/mL of blood meal) in decapitated insects significantly reversed the altered organization of the stomach and intestine. These results point to a brain factor, possibly the prothoracicotropic hormone (PTTH) which stimulates ecdysteroid production in the prothoracic glands, may be a factor responsible, directly or indirectly, for the midgut cell organization in R. prolixus.

Journal Article↗