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Biomedical subjects

J M Ribeiro

Publications and source records attributed to J M Ribeiro.

At least 19 recordsLinked to original sources
PubMed2006

The contribution of extensin network formation to rapid, hydrogen peroxide-mediated increases in grapevine callus wall resistance to fungal lytic enzymes.

Grapevine (Vitis vinifera cv. Touriga) callus cell walls contain a high level of the monomeric extensin, GvP1. Hydrogen peroxide stimulus of these cultures causes the rapid loss of monomeric GvP1, concomitant with marked increases in insoluble GvP1 amino acids and wall resistance to digestion by fungal lytic enzymes. JIM11 immunolocalization studies indicated that monomeric and network GvP1 were evenly distributed in the callus cell wall. These primary cell walls were used to investigate the specific contribution of extensin and other ionically bound cell-wall proteins to hydrogen peroxide-mediated increases in resistance to fungal lytic enzymes. This was performed by removing ionically-bound proteins and assaying for hydrogen peroxide-enhanced resistance after the addition of selected protein fractions. The results indicate that hydrogen peroxide-induced increases in resistance to digestion by fungal lytic enzymes require a co-operative action between network extensin formation and the electrostatic interaction of additional wall proteins with the extracellular matrix.

Cell Wall↗
PubMed2004

[Neocorporatist arrangements and defense of physicians' interests].

In Brazil, the trade union structure created by authoritarian corporatism in the 1930's began to change when the cycle of the military regime installed in 1964 came to an end. With redemocratization, the trade union movement began to coexist with the organization of pluralistic interests, a process which has influenced the physicians' movement since 1977. The new National Constitution adopted in 1988 provided for multipartite control over health policy. We present a conceptual discussion of neocorporatist arrangements (which are common in European social experience) and their significance for an understanding of health policy in the context of the so called Health Reform process in Brazil.

English Abstract↗
PubMed2004

Malaria vaccines: lessons from field trials.

Malaria vaccine candidates have already been tested and new trials are being carried out. We present a brief description of specific issues of validity that are relevant when assessing vaccine efficacy in the field and illustrate how the application of these principles might improve our interpretation of the data being gathered in actual malaria vaccine field trials. Our discussion assumes that vaccine evaluation shares the same general principles of validity with epidemiologic causal inference, i.e., the process of drawing inferences from epidemiologic data aiming at the identification of causes of diseases. Judicious exercise of these principles indicates that, for meaningful interpretation, measures of vaccine efficacy require definitions based upon arguments conditional on the amount of exposure to infection, and specification of the initial and final states in which one believes the effect of interest takes place.

Journal Article↗
PubMed2004

[Autonomy and work in medicine].

We discuss autonomy in medical work as resulting from two basic moments: as social work consuming and producing goods and services, reproducing the dominant mode of production and its ethical foundations; and as a service in which autonomy, limited as social work, expresses some attributes acquired by medical work (technical independence and self-regulation) as a result of the monopoly in the use of science to deal with individually perceived health-related needs. These moments are expressed in the doctor-patient relationship, which makes uncertainties surrounding that relationship more evident. From this understanding about medical work and its autonomous condition, we discuss some theoretical concepts related to the study of labor and/or services in contemporary society and which provide us with an epistemological basis for more adequate approaches to scientific research concerning that object.

English Abstract↗
PubMed2001

Exploring the transcriptome of the malaria sporozoite stage.

Most studies of gene expression in Plasmodium have been concerned with asexual and/or sexual erythrocytic stages. Identification and cloning of genes expressed in the preerythrocytic stages lag far behind. We have constructed a high quality cDNA library of the Plasmodium sporozoite stage by using the rodent malaria parasite P. yoelii, an important model for malaria vaccine development. The technical obstacles associated with limited amounts of RNA material were overcome by PCR-amplifying the transcriptome before cloning. Contamination with mosquito RNA was negligible. Generation of 1,972 expressed sequence tags (EST) resulted in a total of 1,547 unique sequences, allowing insight into sporozoite gene expression. The circumsporozoite protein (CS) and the sporozoite surface protein 2 (SSP2) are well represented in the data set. A BLASTX search with all tags of the nonredundant protein database gave only 161 unique significant matches (P(N) < or = 10(-4)), whereas 1,386 of the unique sequences represented novel sporozoite-expressed genes. We identified ESTs for three proteins that may be involved in host cell invasion and documented their expression in sporozoites. These data should facilitate our understanding of the preerythrocytic Plasmodium life cycle stages and the development of preerythrocytic vaccines.

Amino Acid Motifs↗
PubMed2001

Toward a defined anti-Leishmania vaccine targeting vector antigens: characterization of a protective salivary protein.

Leishmania parasites are transmitted to their vertebrate hosts by infected phlebotomine sand fly bites. Sand fly saliva is known to enhance Leishmania infection, while immunity to the saliva protects against infection as determined by coinoculation of parasites with vector salivary gland homogenates (SGHs) or by infected sand fly bites (Kamhawi, S., Y. Belkaid, G. Modi, E. Rowton, and D. Sacks. 2000. Science. 290:1351-1354). We have now characterized nine salivary proteins of Phlebotomus papatasi, the vector of Leishmania major. One of these salivary proteins, extracted from SDS gels and having an apparent mol wt of 15 kD, was able to protect vaccinated mice challenged with parasites plus SGH. A DNA vaccine containing the cDNA for the predominant 15-kD protein (named SP15) provided this same protection. Protection lasted at least 3 mo after immunization. The vaccine produced both intense humoral and delayed-type hypersensitivity (DTH) reactions. B cell-deficient mice immunized with the SP15 plasmid vaccine successfully controlled Leishmania infection when injected with Leishmania plus SGH. These results indicate that DTH response against saliva provides most or all of the protective effects of this vaccine and that salivary gland proteins or their cDNAs are viable vaccine targets against leishmaniasis.

Amino Acid Sequence↗
PubMed2001

The invertebrate growth factor/CECR1 subfamily of adenosine deaminase proteins.

Adenosine deaminase (ADA) catalyzes the hydrolysis of adenosine to inosine. Its lack determines severe combined immunodeficiency in mammals, possibly due to accumulation of extracellular adenosine, which induces apoptosis in lymphocytes (Franco et al., 1998). Thus, presence of normal levels of ADA leads to normal growth and proliferation of lymphocytes. Several vertebrate and microbial ADA amino-acid sequences are known, with substantial similarity to each other. On the other hand, there are invertebrate growth factors as well as a candidate gene for the human cat eye syndrome (CECR1) (Riazi et al., 2000. Genomics 64, 277-285), which share substantial similarity to each other, and also to ADA. In this study, we report the expression and ADA enzymatic activity of a cDNA from the salivary glands of Lutzomyia longipalpis, a blood-sucking insect, with substantial similarity to insect growth factors and to human CECR1. We also demonstrate the existence of a subfamily of the adenosine deaminase family characterized by their unique amino-terminal region. Both Drosophila melanogaster and humans have both types of adenosine deaminases. Results indicate that these invertebrate proteins previously annotated as growth factors, as well as the human CECR1 gene product, may exert their actions through adenosine depletion. The different roles played by each type of adenosine deaminase in humans and Drosophila remains to be fully investigated.

Adenosine↗
PubMed2001

Human placenta hydrolases active on free ADP-ribose: an ADP-sugar pyrophosphatase and a specific ADP-ribose pyrophosphatase.

Free ADP-ribose has a reducing ribose moiety and it is hazardous due to its nonenzymic reactivity toward protein side chains. ADP-ribose hydrolases are putative protective agents to avoid the intracellular accumulation of ADP-ribose. In mammalian sources, two types of enzymes with ADP-ribose hydrolase activity are known: (i) highly specific ADP-ribose pyrophosphatases, which in a Mg(2+)-dependent fashion hydrolyse only ADP-ribose and the nonphysiological analogue IDP-ribose, and (ii) less specific nucleoside diphosphosugar or diphosphoalcohol (NDP-X) pyrophosphatases, which besides A(I)DP-ribose hydrolyse also some nonreducing NDP-X substrates. So far, of these two enzyme types only the less specific one has been reported in human sources: an ADP-sugar pyrophosphatase purified from erythrocytes or expressed from cDNA clones. Here we report that human placenta extracts contain two ADP-ribose hydrolases, which were characterised after a near 1000-fold purification. One is an ADP-sugar pyrophosphatase: it hydrolysed ADP-ribose, ADP-glucose and ADP-mannose, but not e.g. UDP-glucose, at similar rates. It resembles the erythrocyte and recombinant enzyme(s), but showed a 5-20-fold lower K(m) for ADP-ribose (7 microM). The other enzyme is a highly specific ADP-ribose pyrophosphatase (the first of this kind to be reported in humans): it hydrolysed only ADP-ribose and IDP-ribose at similar rates, with a very low, 0.4 microM K(m) for the former. This is a major candidate to control the accumulation of free ADP-ribose in humans. It remains to be seen whether it belongs to the 'nudix' protein family, which includes several ADP-ribose hydrolases and other 'housecleaning' enzymes (M.J. Bessman, D.N. Frick, S.F. O'Handley, J. Biol. Chem. 271 (1996) 25059-25062).

Adenosine Diphosphate Ribose↗
PubMed2001

The salivary adenosine deaminase activity of the mosquitoes Culex quinquefasciatus and Aedes aegypti.

A cDNA coding for a protein with significant similarity to adenosine deaminase (ADA) was found while randomly sequencing a cDNA library constructed from salivary gland extracts of adult female Culex quinquefasciatus. Prompted by this result, we found high ADA activities in two culicine mosquitoes, Culex quinquefasciatus and Aedes aegypti, but not in the anopheline Anopheles gambiae. Homogenates from Culex quinquefasciatus also have an AMP deaminase activity that is three times greater than the ADA activity, whereas in Aedes aegypti the AMP deaminase activity is less than 10% of the ADA activity. Evidence for secretion of ADA during blood feeding by Aedes aegypti includes the presence of ADA activity in warm solutions probed through a membrane by mosquitoes and in serotonin-induced saliva and a statistically significant reduction in the levels of the enzyme in Aedes aegypti following a blood meal. We could not demonstrate, however, that C. quinquefasciatus secrete ADA in their saliva. Male Aedes aegypti and C. quinquefasciatus, which do not feed on blood, have less than 3% of the levels of ADA found in females. We propose that ADA activity in A. aegypti may help blood feeding by removing adenosine, a molecule associated with both the initiation of pain perception and the induction of mast cell degranulation in vertebrates, and by producing inosine, a molecule that potently inhibits the production of inflammatory cytokines. The role of salivary ADA in Culex quinquefasciatus remains unclear.

AMP Deaminase↗
PubMed2001

The salivary apyrase of the blood-sucking sand fly Phlebotomus papatasi belongs to the novel Cimex family of apyrases.

Apyrases are enzymes that hydrolyze nucleotide di- and triphosphates to orthophosphate and mononucleotides. At least two families of enzymes, belonging to the 5'-nucleotidase and to the actin/heat shock 70/sugar kinase superfamily, have evolved independently to serve the apyrase reaction. Both families require either Ca(2+) or Mg(2+) for their action. A novel apyrase enzyme sequence, with no homology to any other known protein sequence, was found recently in the salivary glands of the hematophagous bed bug Cimex lectularius. This enzyme functions exclusively with Ca(2+). Here, we report the finding of a cDNA similar to that of the C. lectularius salivary apyrase isolated from a salivary gland cDNA library of Phlebotomus papatasi. Transfection of insect cells with the P. papatasi salivary gland apyrase cDNA resulted in the secretion of a Ca(2+)-dependent apyrase whose activity was indistinguishable from that in salivary homogenates of P. papatasi. Homologous sequences were found in humans, in another sand fly (Lutzomyia longipalpis), in the fruit fly Drosophila melanogaster, in the nematode Caenorhabditis elegans and in the protozoan Cryptosporidium parvum, indicating that this family of enzymes is widespread among animal species.

Amino Acid Sequence↗
PubMed2001

Platelet-activating-factor-hydrolyzing phospholipase C in the salivary glands and saliva of the mosquito Culex quinquefasciatus.

A phospholipase C activity specific for platelet-activating factor (PAF), named PAF phosphorylcholine hydrolase, was found in the salivary glands and saliva of the human-feeding mosquito Culex quinquefasciatus. The enzymatic activity was demonstrated by inhibition of PAF-induced platelet aggregation, and by identification of substrate consumption and production of diacyl glyceride by electrospray-ionisation mass spectrometry. The activity has a neutral optimal pH and an apparent molecular mass of 40-50 kDa. Two anthropophilic mosquito species, Aedes aegypti and Anopheles gambiae, do not have this salivary activity. The results are interpreted within the evolutionary context of the genera Culex, Aedes and Anopheles.

Animals↗
PubMed2001

A snake venom phospholipase A(2) blocks malaria parasite development in the mosquito midgut by inhibiting ookinete association with the midgut surface.

Oocyst formation is a critical stage in the development of the malaria parasite in the mosquito. We have discovered that the phospholipase A(2) (PLA2) from the venom of the eastern diamondback rattlesnake (Crotalus adamanteus) inhibits oocyst formation when added to infected chicken blood and fed to mosquitoes. A similar transmission-blocking activity was demonstrated for PLA2s from the venom of other snakes and from the honeybee. This effect is seen both with the avian malaria parasite Plasmodium gallinaceum and with the human parasite Plasmodium falciparum developing in their respective mosquito hosts. The inhibition occurs even in the presence of an irreversible inhibitor of the active site of PLA2, indicating that the hydrolytic activity of the enzyme is not required for the antiparasitic effect. Inhibition is also seen when the enzyme is fed to mosquitoes together with ookinetes, suggesting that the inhibition occurs after ookinete maturation. PLA2 has no direct effect on the parasite. However, pretreatment of midguts with PLA2 (catalytically active or inactive) dramatically lowers the level of ookinete/midgut association in vitro. It appears, therefore, that PLA2 is acting by associating with the midgut surface and preventing ookinete attachment to this surface. Thus, PLA2 is an excellent candidate for expression in transgenic mosquitoes as a means of inhibiting the transmission of malaria.

Aedes↗
PubMed2001

The salivary adenosine/AMP content of Phlebotomus argentipes Annandale and Brunetti, the main vector of human kala-azar.

Adenosine and AMP in the salivary glands of the sand fly Phlebotomus argentipes were characterized by reversed-phase high-pressure liquid chromatography with diode-array detection and mass spectrometry. AMP and adenosine were measured in individual salivary gland pairs, yielding 76.8 +/- 8.6 and 380 +/- 25 pmoles per pair of salivary glands, respectively (mean +/- SE, n = 12). These values decrease to 45 +/- 7 and 181 +/- 21 pmoles following a blood meal, indicating that AMP and adenosine were secreted. Because adenosine and AMP have anti-platelet, vasodilatory, and immunomodulatory properties, it is proposed that these salivary nucleotides help the fly to blood feed and may affect Leishmania transmission.

Adenosine↗
PubMed2000

Purification, cloning, and expression of a novel salivary anticomplement protein from the tick, Ixodes scapularis.

The alternative pathway of complement is an important defense against pathogens and in tick rejection reactions. The tick Ixodes scapularis is able to feed repeatedly on its natural host and has a salivary anticomplement activity that presumably facilitates feeding. In this study, we purified and then obtained the amino-terminal sequence of the I. scapularis salivary anticomplement (Isac). We found a full-length clone coding for Isac by random screening of a salivary gland cDNA library. Expressing Isac cDNA in COS cells reproduced the activity found in tick saliva, namely, inhibition of rabbit erythrocyte lysis by human serum in the presence of Mg(2+) and EGTA, inhibition of C3b binding to agarose in the presence of Mg(2+) and EGTA, and acceleration of factor Bb uncoupling from the C3 convertase generated by the alternative pathway. Recombinant Isac had no effect on the recalcification time of human platelet-poor plasma or in the classical complement pathway, indicating that it is a specific inhibitor similar to the regulators of complement activation of the alternative pathway such as factor H. Isac, however, has no similarity to any protein in the GenBank(TM) data base, indicating that it is a novel and relatively small (18.5 kDa) anticomplement molecule.

Amino Acid Sequence↗
PubMed2000

Delayed-type hypersensitivity to Phlebotomus papatasi sand fly bite: An adaptive response induced by the fly?

The saliva of bloodsucking arthropods contains a large array of pharmacologically active compounds that assist hematophagy. Arthropod saliva is also responsible for causing uncomfortable allergic responses in its vertebrate hosts. In this article, we investigate whether the sand fly Phlebotomus papatasi, known to produce a strong delayed-type hypersensitivity (DTH) in humans, could benefit from, and possibly adaptively induce, this response in their vertebrate hosts. In this study, we show that flies fed on humans to completion nearly twice as fast in DTH sites as compared with normal skin sites. DTH sites had significantly larger blood flow as measured by the laser Doppler method. Sand flies feeding at sites in mouse ears that had a DTH response also fed faster than at normal sites. We conclude that in the case of P. papatasi, and possibly other arthropods such as fleas and bed bugs, the strong saliva-induced DTH response may reflect an adaptation of the fly to manipulate host immunity for the insect's own advantage.

Adaptation, Physiological↗