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Biomedical subjects

M A Sosa

Publications and source records attributed to M A Sosa.

At least 19 recordsLinked to original sources
PubMed2006

A novel icetexane diterpene, 5-epi-icetexone from Salvia gilliessi is active against Trypanosoma cruzi.

In this work the effect of a novel compound, 5-epi-icetexone (ICTX) obtained from Salvia gilliessi Benth. (Labiatae), is studied on cultured epimastigotes of Trypanosoma cruzi (Tulahuen). It was found that the compound exerts an antiproliferative effect on the parasites at concentrations between 2.8 and 4.2 microM, and similar sensitivity in other strains (Dm28c, CL-Brener and Y-strain). The compound was deleterious at concentrations higher than 4.2 microM, with an estimated IC50 of 6.5+/-0.75 microM, but with low cytotoxicity to mammalian cells. These effects were irreversible, even at short times of exposure to the drug. In solution, ICTX showed to be stable for at least 96 h at 29 degrees C. With cytostatic dose a little percentage of parasites was resistant to the action of ICTX, and they continued growing although with different kinetic. By electron transmission microscopy, at dose of 4.2 microM an external vesiculization was observed on the first day of exposure to the compound, but the parasite cytoplasm became plenty of vacuoles and exhibited nuclear disorganization from the second day of exposure. It was concluded that ICTX is active against T. cruzi and may act by multiple mechanisms. In future, this novel icetexane diterpene may be a good candidate for therapeutic use against Chagas' disease.

Animals↗
PubMed2005

Developmental differences between cation-independent and cation-dependent mannose-6-phosphate receptors in rat brain at perinatal stages.

Mannose-6-phosphate receptors (MPRs) play a role in the selective transport of macromolecules bearing mannose-6-phosphate residue to lysosomes. To date, two types of MPRs have been described in most of cells and tissues: the cation-dependent (CD-MPR) and cation-independent mannose-6-phosphate receptor (CI-MPR). In order to elucidate their possible role in the central nervous system, the expression and binding properties of both MPRs were studied in rat brain along perinatal development. It was observed that the expression of CI-MPR decreases progressively from fetuses to adults, while the CD-MPR increases around the 10th day of birth, and maintains these values up to adulthood. Binding assays showed differences in the Bmax and KD values between the ages studied, and they did not correlate with the expression levels of both MPRs. Variations in lysosomal enzyme activities and expression of phosphomannosylated ligands during development correlated more with CD-MPR than with CI-MPR expression. These results suggest that both receptors play a different role in rat brain during perinatal development, being CD-MPR mostly involved in lysosome maturation.

Age Factors↗
PubMed2005

Binding of AP-2 adaptor complex to brain membrane is regulated by phosphorylation of proteins.

Phosphorylation of proteins appears as a key process in early steps of clathrin coated vesicle formation. Here, we report that treatment of post-nuclear fraction with alkaline phosphatase induced redistribution of alpha subunits of AP-2 adaptor complex to cytosol and this effect was higher in the alpha2 subunit. A high serine phosphorylation status of alpha subunits correlated with the higher affinity of AP-2 to membranes. Using a simple binding assay, where membranes were incubated with either purified adaptors or cytosols, we observed an inhibitory effect of tyrphostin, a tyrosine kinase inhibitor, on the binding of AP-2 to membranes, but also an unexpected decrease induced by the phosphatase inhibitor cyclosporine. We also show an inhibitory effect of ATP mediated by cytosolic proteins, although it could not be related to the phosphorylation of AP-2, suggesting an action upstream a cascade of phosphorylations that participate in the regulation of the assembly of AP-2 to membranes.

Adaptor Protein Complex 2↗
PubMed2003

Prolonged ethanol ingestion decreases alpha-mannosidase activity and induces its redistribution to the fluid phase in rat cauda epididymis.

The role of glycosidases in mammalian epididymal fluid is still a controvertial subject. There exists a body of evidence in favour of a function in remodeling the sperm surface as one step in gamete maturation, whilst others argue in favor of an extraepididymal role for these enzymes. In this study we measured the activity and distribution of four glycosidases in rat cauda epididymis after prolonged ethanol ingestion, a condition associated with fertility disturbances. We found that alpha-mannosidase is the most sensitive enzyme to the stress caused by alcohol, since its activity in epididymis significantly decreased and partly redistributed from the spermatozoa to the fluid phase. From these results we suggested that alcohol treatment affects the expression of the enzyme and possibly induces a loss of interaction with the affinity sites on the sperm surface. Although other enzymes also underwent changes due to the alcohol treatment, we focussed on the importance of alpha-mannosidase in the fertilizing capability of spermatozoa.

Alcohol Drinking↗
PubMed2001

The calcium chelator BAPTA affects the binding of assembly protein AP-2 to membranes.

Clathrin coated vesicles are involved in receptor-mediated transport. The coat of these vesicles is constituted mostly of clathrin and the assembly proteins AP-1 or AP-2. In the present study using an in vitro binding system, we found that the interaction of AP-2 but not AP-1 with membranes diminished when the calcium chelating agent BAPTA was added. The maximal inhibitory effect was observed with 10 mM of the chelating agent. Binding of AP-2 to membranes was recovered by adding calcium in a concentration-dependent fashion. Binding was also affected when the membranes were previously treated with BAPTA and then washed. However, other chelating agents such as EDTA or EGTA, as well as the zinc chelating TPEN, did not have any effect on the binding. From these results we postulate a role for calcium in regulating the assembly-disassembly cycle of adaptors in the formation of clathrin coated vesicles.

Adaptor Proteins, Vesicular Transport↗
PubMed2000

Purification of proteins from rat sperm membranes that interact with ligands other than phosphomannosyl residues.

In this study proteins were purified from rat sperm membranes which might be the high affinity sites for ligands of epididymal fluid other than the mannose-6-phosphate receptors. The sperm membrane proteins were solubilized and passed over an affinity column containing epididymal fluid proteins coupled to a matrix. Two bands in the range of 45-55 kDa were eluted from the column with fructose-6-phosphate but not with mannose-6-phosphate. Although the molecular weight of these proteins are similar to those of the cation-dependent phosphomannosyl receptors they are not related. These two proteins may correspond either to two different receptors or to forms of the same receptor that recognize ligands from rat epididymal fluid. Sequencing and identification of these proteins will be the aim of future studies.

Animals↗
PubMed2000

Changes in distribution of phosphomannosyl receptors during maturation of rat spermatozoa.

The aim of the present work was to study the distribution of the cation-independent (CI) and cation-dependent (CD) mannose-6-phosphate receptors (MPRs) in spermatozoa obtained from either rete testis or three regions of rat epididymis. We observed that both receptors underwent changes in distribution as spermatozoa passed from rete testis to cauda epididymis. CI-MPR was concentrated in the dorsal region of the head in rete testis sperm and that this labeling extended to the equatorial segment of epididymal spermatozoa. CD-MPR, however, changed from a dorsal distribution in rete testis, caput, and corpus to a double labeling on the dorsal and ventral regions in cauda spermatozoa. The percentages of spermatozoa that showed staining for either CI-MPR or CD-MPR increased from rete testis to epididymis. The observed changes were probably the result of a redistribution during transit rather than an unmasking of receptors. The fluorescence corresponding to CD-MPR and CI-MPR on the dorsal region disappeared when caudal spermatozoa underwent the acrosomal reaction. Receptors were localized on the plasmalemma of spermatozoa, as observed by immunoelectron microscopy. Changes in distribution may be related to a maturation process, which suggests new roles for the phosphomannosyl receptors.

Animals↗
PubMed2000

The sesquiterpene lactone dehydroleucodine (DhL) affects the growth of cultured epimastigotes of Trypanosoma cruzi.

Here, we report an inhibitory effect of a sesquiterpene lactone dehydroleucodine (DhL) on the growth of Trypanosoma cruzi in culture. At concentrations of the drug between 5 and 10 microg/ml in the medium,the parasites remained alive for at least 4 days. Higher concentrations of DhL were lethal for the parasites within a few hours. The effect of DhL is irreversible. Morphological changes induced by DhL were also observed in the parasites. The effect of DhL was blocked by the presence of reducing substrates such as glutathione or dithiothreitol, but these agents were not able to reverse the effect of DhL if added 2 days after the start of drug exposure.

Animals↗
PubMed1998

alpha-Mannosidase from rat epididymal fluid is a ligand for phosphomannosyl receptors on the sperm surface.

This study demonstrates that alpha-mannosidase from rat epididymal fluid is a ligand for phosphomannosyl receptors on the sperm surface. This enzyme was bound to intact epididymal spermatozoa with high affinity and in saturable form, and the binding was inhibited by mannose-6-phosphate but not by phosphorylated derivatives of fructose. Treatment of the enzyme with sodium periodate inhibited the binding of alpha-mannosidase, confirming that a carbohydrate residue is involved in the interaction with spermatozoa. Evidence is also presented that the cation-independent phosphomannosyl receptors are responsible for the interaction with alpha-mannosidase. These findings suggest a new role for extracellular transport mediated by the mannose-6-phosphate receptor.

Animals↗
PubMed1998

Changes in the content of rat epididymal fluid induced by prolonged treatment with tamoxifen.

Prolonged treatment with tamoxifen induces changes in the male reproductive tract in rats. In this study changes in the protein content of the rat epididymal fluid as a consequence of prolonged treatment with tamoxifen are reported. Among five lysosomal enzymes measured in the epididymal fluid, alpha-mannosidase (alpha-MAN) significantly diminished, but other enzymes did not. Electrophoretic analysis of fluids showed that proteins of estimated molecular weight 25, 60, 80-85 and 180 kDa decreased in the treated rats. We also detected an increase in the binding of beta-galactosidase (beta-GAL) to caudal spermatozoa in treated rats. These changes may be related in part to the loss of fertilizing capacity of spermatozoa after tamoxifen treatment.

Animals↗
PubMed1997

Is an ATPase involved in uncoating of plasma membrane adaptor complex AP-2?

The coat of clathrin-coated vesicles mostly consists of clathrin and adaptor complexes AP-1 or AP-2. Clathrin is released from the vesicles in an ATP-dependent fashion prior to their fusion with endosomes. In the present study we found that ATP strongly inhibits in vitro binding of cytosolic AP-2 to membranes of stripped vesicles, and promotes the release of endogenous AP-2 from clathrin-deprived coated vesicles. Both effects required hydrolysis of ATP. In contrast, binding of AP-1 to stripped vesicles was not affected by ATP, but was enhanced by GTP-gamma-S. These results point to an ATPase that promotes the release of AP-2 from clathrin-coated vesicles.

Acyl Coenzyme A↗
PubMed1997

Growth cones turn up concentration gradients of diffusible peripheral target-derived factors.

Severed peripheral nerve axons grow across a gap in their pathway to regenerate into the distal nerve stump. At the turn of the century this observation led to the proposal that concentration gradients of factors released from the cells of the distal nerve segment orient the growth of the regenerating axons. Recently, several central nervous system target-derived factors have been shown to direct process outgrowth via concentration gradients of the factors during development. The demonstration of target-derived tropic influences in the peripheral nervous system has however remained elusive. We have examined whether concentration gradients of diffusible factors released by the cells of a length of peripheral nerve influence the outgrowth of adult sensory neuron growth cones in vitro. We demonstrate that the growth cones turn and grow up the concentration gradients, providing evidence for the presence of diffusible peripheral target-derived neurotropic factors that can act in the peripheral nervous system.

Animals↗
PubMed1996

A human kidney cDNA which induces a cell surface protein epitope recognized by a monoclonal antibody against galactosylceramide.

Antibodies against the myelin glycolipid galactosylceramide are widely used to study the distribution and function of this molecule. However, anti-galactosylceramide antibodies are not monospecific and have been shown to recognize epitopes carried not only by other glycolipids, but also by proteins. Using expression cloning we have identified a human kidney cDNA which induces a cell-surface protein recognized by the anti-galactosylceramide monoclonal antibody R-mab. These findings further support the idea that cross-reactive proteins may mediate some of the biological effects of the anti galactosylceramide antibodies.

Amino Acid Sequence↗
PubMed1996

Specificity of identified central synapses in the embryonic cockroach: appropriate connections form before the onset of spontaneous afferent activity.

The mechanisms by which neurons recognize the appropriate postsynaptic cells remain largely unknown. A useful approach to this problem is to use a system with a few identifiable neurons that form highly specific synaptic connections. We studied the development of synapses between two identified cercal sensory afferents and two giant interneurons (GIs) in the embryonic cockroach Periplaneta americana. By 46% of embryonic development, the axons of the filiform hair sensory neurons have entered the terminal ganglionic neuropil and grow alongside the GI primary dendrites, although they do not form synapses. From 50% of development, the GI dendrites grow outward from the center of the neuropil to contact the presynaptic axons and their branches. The sensory neurons begin to spike at 52% of development, and, from 55% of development, these action potentials evoked excitatory postsynaptic potentials in the GIs. Synaptic contacts were first seen at this time. The pattern of synaptic connections was highly specific from the outset. G12 had strong input from the medial (M) afferent and had almost negligible input from the lateral (L) afferent, whereas G13 had input from both. This specificity was present before bursts of spontaneous activity began in the sensory neurons at 59% of development. G12 filopodia selectively formed synaptic contacts with the M axon rather than the L axon. The few contacts made by G12 with the L axon had a normal morphology but fewer presynaptic densities. Filopodial insertions were not involved in selective synapse formation. In this system, highly specific synaptic recognition appears to be activity independent.

Animals↗
PubMed1996

Changes in N-acetyl-beta-D-glucosaminidase binding system in rat liver during growth.

In this paper, we characterize the binding of N-acetyl-beta-D-glucosaminidase to membranes of rat liver during development. Cation-independent phosphomannosyl receptors were shown to be involved in the recognition of the enzyme at the following ages: 18 days of fetal life, 10-, 30- and 90-day-old rats. We remark here two important differences in the binding of the fetal enzyme when compared with that in 90-day-old rats; (a) in addition to an optimal binding at pH 7.0, the fetal enzyme showed another peak of binding at acidic pH (5.0), and (b) the binding of the fetal enzyme was also inhibited by galactose-6-phosphate. This inhibition was higher than that of mannose-6-phosphate at the acidic pH. We concluded that the lysosomal enzymes and their receptors undergo important changes around birth.

Acetylglucosaminidase↗
PubMed1996

Identifying a new reality: zero vascular access recirculation using ultrasound dilution.

Access recirculation measurements by blood urea nitrogen (BUN) sampling methods have come under recent criticism regarding their reliability especially at low levels of recirculation. New methods have shown that the majority of patients have much less recirculation than previously suspected. However, some of these methods are prone to the same factors that limit BUN measurement accuracy. A new method, ultrasound dilution, was studied that avoids these problems and supports a new clinical reality--zero access recirculation. Information on the relationship of recirculation to access flow was also obtained which supports the assumption that patients with adequate vascular access flows have no recirculation.

Adult↗
PubMed1995

Lysosomal enzyme activity in rat adrenal gland related to the postnatal development.

The activity of five acid hydrolases in the adrenal gland at the perinatal stage in adult rats was measured here and changes in alpha-mannosidase and N-acetyl-beta-D- glucosaminidase activity were detected. These enzymes increase after birth reaching a peak between days 4 and 7. Other enzymes such as beta-glucuronidase, arylsulfatase and beta-glucosidase did not significantly change at the ages studied. These data suggest that the enzymatic activity and development of the adrenal gland may be correlated during the first week after birth; this is critical since most of the changes occur in this organ.

Acetylglucosaminidase↗