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S López

Publications and source records attributed to S López.

At least 73 records · Page 4Linked to original sources
PubMed1998

A new cysteine in rotavirus VP4 participates in the formation of an alternate disulfide bond.

Most animal rotaviruses bind to a cell surface molecule that contains sialic acid (SA). We have recently isolated variants from simian rotavirus RRV which show an SA-independent phenotype. The VP4 protein of these variants was shown to have three amino acid changes with respect to the wt protein, one of them being Tyr-267 --> Cys. In this work, we have investigated whether the new cysteine could interfere with the disulfide bond (Cys-318/Cys-380) present in the VP5* subunit of the wt protein. Cysteine residues 318 and 380 were mutagenized in gpr8 and RRV VP4 genes, and the wt and mutant genes were transcribed and translated in vitro. The protein products were analysed by electrophoresis under reducing and non-reducing conditions. This approach showed that, in the VP4 protein synthesized in vitro, Cys-267 is capable of forming an alternate disulfide bond with Cys-318. This alternate bond also seems to occur in the VP4 protein present in the variant gpr8 virus particles.

Amino Acid Substitution↗
PubMed1998

Serotype specificity of the neutralizing-antibody response induced by the individual surface proteins of rotavirus in natural infections of young children.

The relative contribution of the rotavirus surface proteins, VP4 and VP7, to the induction of homotypic as well as heterotypic neutralizing antibodies (NtAbs) in natural infections was studied. The NtAb titers of paired sera from 70 infants with serologically defined primary rotavirus infections were determined with a panel of rotavirus reassortants having one surface protein from a human rotavirus (serotypes G1 to G4 for VP7 and P1A and P1B for VP4) and the other surface protein from a heterologous animal rotavirus strain. A subset of 37 children were evaluated for epitope-specific antibodies to the two proteins by an epitope-blocking assay. The infants were found to seroconvert more frequently to VP4 than to VP7 by both methods, although the titers of the seroconverters were higher to VP7 than to VP4. Both proteins induced homotypic as well as heterotypic NtAbs. G1 VP7 frequently induced a response to both G1 and G3 VP7s, while G3 VP7 and P1A VP4 induced mostly homotypic responses.

Antibodies, Monoclonal↗
PubMed1998

Antigenic and genomic diversity of human rotavirus VP4 in two consecutive epidemic seasons in Mexico.

In the present investigation we characterized the antigenic diversity of the VP4 and VP7 proteins in 309 and 261 human rotavirus strains isolated during two consecutive epidemic seasons, respectively, in three different regions of Mexico. G3 was found to be the prevalent VP7 serotype during the first year, being superseded by serotype G1 strains during the second season. To antigenically characterize the VP4 protein of the strains isolated, we used five neutralizing monoclonal antibodies (MAbs) which showed specificity for VP4 serotypes P1A, P1B, and P2 in earlier studies. Eight different patterns of reactivity with these MAbs were found, and the prevalence of three of these patterns varied from one season to the next. The P genotype of a subset of 52 samples was determined by PCR. Among the strains characterized as genotype P[4] and P[8] there were three and five different VP4 MAb reactivity patterns, respectively, indicating that the diversity of neutralization epitopes in VP4 is greater than that previously appreciated by the genomic typing methods.

Antibodies, Monoclonal↗
PubMed1998

[Phenotypic characterization of erythromycin resistance in strains of the genus Streptococcus isolated from clinical specimens].

There are presently two recognized mechanisms of resistance to macrolide antibiotics in species of the genus Streptococcus: target modification and efflux. Target modification occurs in the ribosomes through the production of a ribosomal methylase codified for the erm genes and it is phenotypically known as MLSB resistance. Expression of MLSB resistance can be inducible or constitutive. Active efflux has been recently described in S. pyogenes and S. pneumoniae, and its expression is known as M phenotype. We studied the susceptibility, by determining the MIC using agar dilution, to penicillin, erythromycin and clindamycin, of 295 strains of the genus Streptococcus clinically isolated from 1993 to 1996 (70 S. pyogenes, 81 S. pneumoniae, 37 viridans group, and 107 S. milleri). We also studied the phenotype pattern of erythromycin-clindamycin resistance in the strains resistant to erythromycin by using the double-disc test. We found a 17.2% resistance to erythromycin and a 12.5% resistance to clindamycin. The M phenotype, initially described in S. pyogenes, was also observed in 6.6% of our S. pneumoniae strains, 25% of S. viridans spp., and 4.8% in the S. milleri group.

Anti-Bacterial Agents↗
PubMed1998

Bioavailability of S(+)-ketoprofen after oral administration of different mixtures of ketoprofen enantiomers to dogs.

Recent reports have disagreed on whether the bioavailability of S(+)-ketoprofen is affected by the presence of R(-)-ketoprofen. To examine this directly, we designed a randomized crossover study in beagle dogs. [14C]-S(+)-ketoprofen trometamol and R(-)-ketoprofen trometamol were administered in the following percentage ratios: A, 99:1; B, 95:5; C, 90:10; D, 70:30; E, 50:50. Treatments were administered as a single oral dose of 1 mg/kg tromnetamol salt. Each of eight dogs received all five combinations in random order with a 1-week wash-out period between doses. Blood samples were taken before drug administration and at regular intervals for 240 min after dosing. A progressive increase in the plasma concentration of [14C]-S(+)-ketoprofen was observed on going from treatment E (lowest dose of Senantiomer) to treatments containing the highest doses of [14C]-S(+)-ketoprofen. When the pharmacokinetic calculations were normalized to the dose of [14C]-S(+)-ketoprofen, we found no statistically significant differences among the normalized AUC and Cmax values of the five treatments. Therefore, S(+)-ketoprofen absorption was linear and was not influenced by the presence of R(-)-ketoprofen. Furthermore, there were no significant differences in tmax values among treatments, indicating that the rate of S(+)-ketoprofen absorption was also unaffected by the presence of R(-)-ketoprofen.

Administration, Oral↗
PubMed1997

Prolonged persistence of Listeria monocytogenes after intragastric infection in corticosteroid-treated mice.

In an attempt to obtain a model more closely resembling natural listeriosis, we studied the course of infection in mice inoculated by the intragastric route with Listeria monocytogenes. Corticosteroid-treated, and untreated mice both developed subclinical infection without mortality, but faecal shedding and persistence of bacteria in the liver and spleen of corticosteroid-treated mice were significantly more protracted than in untreated mice. Untreated mice cleared the bacteria from their livers and spleens by day 5 postinfection (PI), whereas treated mice did not clear the organisms until 8-9 days PI. In untreated mice faecal shedding lasted 5 days PI, whereas in treated mice the organisms were recovered at significantly higher levels until day 9 PI. The only intestinal lesions observed were mild pyogranulomatous changes in the dome area of some Peyer's patches in treated mice.

Animals↗
PubMed1997

Synthesis and antimalarial effects of phenothiazine inhibitors of a Plasmodium falciparum cysteine protease.

Acridinediones have previously been shown to have potent antimalarial activity. A series of sulfur isosteres of acridinediones have been synthesized and evaluated for their inhibition of the Plasmodium falciparum cysteine protease falcipain and for their antimalarial activity. A number of these phenothiazines inhibited falcipain and demonstrated activity against cultured P. falciparum parasites at low micromolar concentrations. We propose that the compounds exerted their antimalarial effects by two mechanisms, one of which involves the inhibition of falcipain and a consequent block in parasite degradation of hemoglobin. These compounds and related phenothiazines are worthy of further study as potential antimalarial agents.

Animals↗
PubMed1997

Penetration of Listeria monocytogenes in mice infected by the oral route.

In this study, it is suggested that the Peyer's patches are the most important point of entry of Listeria monocytogenes in the host after subclinical infection by the oral route. Microbiological, histopathological and ultrastructural evidence of infection was obtained in mice inoculated with a sublethal dose of 10(9) cfu. No mortality was observed. L. monocytogenes was isolated from the mesenteric lymph nodes from 6 hours post infection (hpi) through day 7 p.i. and from the liver and spleen from 24 h p.i. until days 5 and 7 p.i. respectively. Lesions were mainly restricted to the dome area of Peyer's patches and consisted of a purulent to pyogranulomatous inflammatory reaction. Scarce and minor lesions were also observed in the mesenteric lymph nodes and liver. L. monocytogenes was detected by immunohistochemistry in the Peyer's patches from 12 h p. i. to day 6 p.i. Ultrastructural study of Peyer's patches showed that the majority of Listeria cells were free within the cytoplasm of neutrophils and macrophages, not surrounded by a phagosomal membrane, and some of them were dividing.

Animals↗
PubMed1997

Identification and characterization of homofermentative mesophilic Lactobacillus strains isolated from artisan starter-free cheeses.

Fifty-six strains of mesophilic lactobacilli from hand-made cheeses made without starters have been isolated, identified and characterized. Of these, 21 strains were classified as Lactobacillus plantarum, 18 as Lact. casei subsp. pseudoplantarum, 10 as Lact. curvatus, five as Lact. casei subsp. casei, and two remained unidentified. The numerical classification of these strains, based on 80 different physiological and morphological characteristics, correlated well with the phenotypic classification. Most of the technologically important traits have been examined in these strains, which will allow the selection of some of them to be tested as adjunct cultures in the manufacture of dairy products.

Bacterial Typing Techniques↗
PubMed1997

Rotaviruses induce an early membrane permeabilization of MA104 cells and do not require a low intracellular Ca2+ concentration to initiate their replication cycle.

In this work, we found that rotavirus infection induces an early membrane permeabilization of MA104 cells and promotes the coentry of toxins, such as alpha-sarcin, into the cell. This cell permeability was shown to depend on infectious virus and was also shown to be virus dose dependent, with 10 infectious particles per cell being sufficient to achieve maximum permeability; transient, lasting no more than 15 min after virus entry and probably occurring concomitantly with virus penetration; and specific, since cells that are poorly permissive for rotavirus were not permeabilized. The rotavirus-mediated coentry of toxins was not blocked by the endocytosis inhibitors dansylcadaverine and cytochalasin D or by the vacuolar proton-ATPase inhibitor bafilomycin A1, suggesting that neither endocytocis nor an intraendosomal acidic pH or a proton gradient is required for permeabilization of the cells. Compounds that raise the intracellular concentration of calcium ([Ca2+]i) by different mechanisms, such as the calcium ionophores A23187 and ionomycin and the endoplasmic reticulum calcium-ATPase inhibitor thapsigargin, did not block the coentry of alpha-sarcin or affect the onset of viral protein synthesis, suggesting that a low [Ca2+]i is not essential for the initial steps of the virus life cycle. Since the entry of alpha-sarcin correlates with virus penetration in all parameters tested, the assay for permeabilization to toxins might be a useful tool for studying and characterizing the route of entry and the mechanism used by rotaviruses to traverse the cell membrane and initiate a productive replication cycle.

Abrin↗
PubMed1997

Functional and structural analysis of the sialic acid-binding domain of rotaviruses.

The infectivity of most animal rotaviruses is dependent on the interaction of the virus spike protein VP4 with a sialic acid (SA)-containing cell receptor, and the SA-binding domain of this protein has been mapped between amino acids 93 and 208 of its trypsin cleavage fragment VP8. To identify which residues in this region are essential for the SA-binding activity, we performed alanine mutagenesis of the rotavirus RRV VP8 expressed in bacteria as a fusion polypeptide with glutathione S-transferase. Tyrosines were primarily targeted since tyrosine has been involved in the interaction of other viral hemagglutinins with SA. Of the 15 substitutions carried out, 10 abolished the SA-dependent hemagglutination activity of the protein, as well as its ability to bind to glycophorin A in a solid-phase assay. However, only alanine substitutions for tyrosines 155 and 188 and for serine 190 did not affect the overall conformation of the protein, as judged by their interaction with a panel of conformationally sensitive neutralizing VP8 monoclonal antibodies (MAbs). These findings suggest that these three amino acids play an essential role in the SA-binding activity of the protein, presumably by interacting directly with the SA molecule. The predicted secondary structure of VP8 suggests that it is organized as 11 beta-strands separated by loops; in this model, Tyr-155 maps to loop 7 while Tyr-188 and Ser-190 map to loop 9. The close proximity of these two loops is also supported by previous results from competition experiments with neutralizing MAbs directed at RRV VP8.

Alanine↗
PubMed1997

Epizootic disseminated toxoplasmosis in captive slender-tailed meerkats (Suricata suricatta).

Fatal disseminated toxoplasmosis was diagnosed in seven captive slender-tailed meerkats (Suricata suricatta) according to clinicopathologic findings and immunohistochemistry. Five of nine meerkats died during an outbreak in late 1994. These included four kits (2.5 to 4.5 months old) and a 4-year-old meerkat. Two other meerkats, both adults, died in 1992 and 1995. Respiratory insufficiency (4/7) and incoordination (3/7) were the most consistent clinical signs. although two of seven meerkats died unexpectedly. At necropsy, the lungs were reddened and noncollapsed (6/7), and had multiple pale round foci (4/7). Yellow foci of necrosis in mesenteric lymph nodes (4/7), splenomegaly (3/7), and hydropericardium (3/7) were other common gross findings. Microscopically, interstitial pneumonia was present in all seven meerkats, being acute to subacute in six of them. Type 2 pneumocyte hyperplasia, aggregates of foamy macrophages, and giant cells were consistently seen. Multifocal to locally extensive necrosis of mesenteric lymph nodes (4/7), mild to severe multifocal necrotizing hepatitis (5/6), and mild nonsuppurative encephalitis (4/6) were also seen. Toxoplasma-like organisms were consistently associated with these lesions and were stained by the avidin biotin peroxidase procedure with an antiserum that does not cross-react with Neospora caninum. Meerkats were most likely infected after an oral, primary exposure to Toxoplasma. Several observations indicate that meerkats may be highly susceptible to toxoplasmosis.

Animals↗
PubMed1997

[The efficacy of interferon alfa treatment in chronic hepatitis C in relation to the serum concentration of RNA-HCV and the viral genotype].

BACKGROUND: To determinate the viral variables (viremia and genotype) and patients variables (route and years of infection, histology, etc) related with response to the treatment with alpha intefferon in patients with chronic hepatitis C. SUBJECTS AND METHODS: We have studied 50 patients with chronic hepatitis C that received an intefferon treatment during a year. In all them it was accomplished a hepatic biopsy before of the beginning of treatment and it was studied the viral load by quantitative PCR (Monitor, Roche) at the beginning of treatment, at four weeks and at the end of treatment. It was determined the HCV genotype by method INNO-LIPA (Boehringer Inghelheim). RESULTS: 8 patients (16%) achieved a complete sustained response during all the follow-up period (13.8 + 1.6 months); 8 patients responded but relapsed when the intefferon was interrupted and 34 patients not responded. The responders had lower viremia (p < 0.032) and HCV RNA negative at the fourth treatment week (p < 0.0082). The genotype 1b was the most frequent, the one which was presenting a smaller percentage of response and it was associated with a higher viremia. Cirrhotic patients were the worse responders. Ex-lDAs were better responders than the others groups, however this difference did not show statistics meaning. CONCLUSIONS: A low pretreatment HCV-RNA level seems to be indicative of a sustained response to IFN, Whereas a high level seems to be indicative of a non sustained response to IFN. Negativization of HCV-RNA at week four is a good indicator of response to intefferon. Genotype 1b is the most frequent and the worse responder. To have 1b genotype, high pretreatment HCV-RNA level and to be viremic at four treatment seems to be indicative of non response.

Adult↗
PubMed1996

Hepatocyte growth factor and transforming growth factor beta regulate 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase gene expression in rat hepatocyte primary cultures.

Hepatocyte growth factor (HGF) and transforming growth factor beta (TGF-beta) are believed to be of major importance for hepatic regeneration after liver damage. We have studied the effect of these growth factors on fructose 2,6-bisphosphate (Fru-2,6-P2) levels and the expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (6PF2K/Fru-2,6-BPase) in rat hepatocyte primary cultures. Our results demonstrate that HGF activates the expression of the 6PF2K/Fru-2,6-BPase gene by increasing the levels of its mRNA. As a consequence of this activation, the amount of 6PF2K/Fru-2,6-BPase protein and 6-phosphofructo-2-kinase activity increased, which was reflected by a rise in Fru-2,6-P2 levels. In contrast, TGF-beta decreased the levels of 6PF2K/Fru-2,6-BPase mRNA, which led to a decrease in the amount of 6PF2K/Fru-2,6-BPase protein and Fru-2,6-P2. The different actions of HGF and TGF-beta on 6PF2K/Fru-2,6-BPase gene expression are concomitant with their effect on cell proliferation. Here we show that, in the absence of hormones, primary cultures of hepatocytes express the F-type isoenzyme. In addition, HGF increases the expression of this isoenzyme, and dexamethasone activates the L-type isoform. HGF and TGF-beta were able to inhibit this activation.

Animals↗
PubMed1996

Interactions between the two surface proteins of rotavirus may alter the receptor-binding specificity of the virus.

The infection of target cells by most animal rotavirus strains requires the presence of sialic acids (SAs) on the cell surface. We recently isolated variants from simian rotavirus RRV whose infectivity is no longer dependent on SAs and showed that the mutant phenotype segregates with the gene coding for VP4, one of the two surface proteins of rotaviruses (the other one being VP7). The nucleotide sequence of the VP4 gene of four independently isolated variants showed three amino acid changes, at positions 37 (Leu to Pro), 187 (Lys to Arg), and 267 (Tyr to Cys), in all mutant VP4 proteins compared with RRV VP4. The characterization of revertant viruses from two independent mutants showed that the arginine residue at position 187 changed back to lysine, indicating that this amino acid is involved in the determination of the mutant phenotype. Surprisingly, sequence analysis of reassortant virus DS1XRRV, which depends on SAs to infect the cell, showed that its VP4 gene is identical to the VP4 gene of the variants. Since the only difference between DS1XRRV and the RRV variants is the parental origin of the VP7 gene (human rotavirus DS1 in the reassortant), these findings suggest that the receptor-binding specificity of rotaviruses, via VP4, may be influenced by the associated VP7 protein.

Animals↗