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Biomedical subjects

E Lázaro

Publications and source records attributed to E Lázaro.

12 recordsLinked to original sources
PubMed2006

Population bottlenecks in quasispecies dynamics.

The characteristics of natural populations result from different stochastic and deterministic processes that include reproduction with error, selection, and genetic drift. In particular, population fluctuations constitute a stochastic process that may play a very relevant role in shaping the structure of populations. For example, it is expected that small asexual populations will accumulate mutations at a higher rate than larger ones. As a consequence, in any population the fixation of mutations is accelerated when environmental conditions cause population bottlenecks. Bottlenecks have been relatively frequent in the history of life and it is generally accepted that they are highly relevant for speciation. Although population bottlenecks can occur in any species, their effects are more noticeable in organisms that form large and heterogeneous populations, such as RNA viral quasispecies. Bottlenecks can also positively select and isolate particles that still keep the ability to infect cells from a disorganized population created by crossing the error threshold.

Base Sequence↗
PubMed2005

Foot-and-mouth disease virus evolution: exploring pathways towards virus extinction.

Foot-and-mouth disease virus (FMDV) is genetically and phenotypically variable. As a typical RNA virus, FMDV follows a quasispecies dynamics, with the many biological implications of such a dynamics. Mutant spectra provide a reservoir of FMDV variants, and minority subpopulations may become dominant in response to environmental demands or as a result of statistical fluctuations in population size. Accumulation of mutations in the FMDV genome occurs upon subjecting viral populations to repeated bottleneck events and upon viral replication in the presence of mutagenic base or nucleoside analogs. During serial bottleneck passages, FMDV survive during extended rounds of replication maintaining low average relative fitness, despite linear accumulation of mutations in the consensus genomic sequence. The critical event is the occurrence of a low frequency of compensatory mutations. In contrast, upon replication in the presence of mutagens, the complexity of mutant spectra increases, apparently no compensatory mutations can express their fitness-enhancing potential, and the virus can cross an error threshold for maintenance of genetic information, resulting in virus extinction. Low relative fitness and low viral load favor FMDV extinction in cell culture. The comparison of the molecular basis of resistance to extinction upon bottleneck passage and extinction by enhanced mutagenesis is providing new insights in the understanding of quasispecies dynamics. Such a comparison is contributing to the development of new antiviral strategies based on the transition of viral replication into error catastrophe.

Biological Evolution↗
PubMed2004

Increase of resistance to macrolides in invasive Streptococcus pneumoniae in Spain (2000-2001).

This study examined the antimicrobial resistance of 1,278 invasive Streptococcus pneumoniae isolates from 41 Spanish laboratories participating in the European Antimicrobial Resistance Surveillance System (EARSS) during 2000 and 2001. Twenty-nine laboratories participated during both years and provided 950 of the isolates. Each laboratory used its own susceptibility testing methods. External quality assessment was performed annually by each participating laboratory. Significant increases in penicillin and erythromycin resistance were observed between 2000 and 2001. This increase was particularly noticeable in isolates from the laboratories participating during both years and in isolates from children and elderly patients.

Adolescent↗
PubMed2002

Characterization of sparsomycin resistance in Streptomyces sparsogenes.

The antitumor antibiotic sparsomycin, produced by Streptomyces sparsogenes, is a universal translation inhibitor that blocks the peptide bond formation in ribosomes from all species. Sparsomycin-resistant strains were selected by transforming the sensitive Streptomyces lividans with an S. sparsogenes library. Resistance was linked to the presence of a plasmid containing an S. sparsogenes 5.9-kbp DNA insert. A restriction analysis of the insert traced down the resistance to a 3.6-kbp DNA fragment, which was sequenced. The analysis of the fragment nucleotide sequence together with the previous restriction data associate the resistance to srd, an open reading frame of 1,800 nucleotides. Ribosomes from S. sparsogenes and the S. lividans-resistant strains are equally sensitive to the inhibitor and bind the drug with similar affinity. Moreover, the drug was not modified by the resistant strains. However, resistant cells accumulated less antibiotic than the sensitive ones. In addition, membrane fractions from the resistant strains showed a higher capacity for binding the drug. The results indicate that resistance in the producer strain is not connected to either ribosome modification or drug inactivation, but it might be related to an alteration in the sparsomycin permeability barrier.

Antibiotics, Antineoplastic↗
PubMed2000

Immunocytochemical localization of the metabotropic glutamate receptor mGluR4a in the piriform cortex of the rat.

This study evaluates the localization of the metabotropic glutamate receptor mGluR4a in the piriform cortex of rats using preembedding immunocytochemical methods. At the light microscopic level, punctate labeling was evident in layers Ia and Ib of the piriform cortex, and immunolabeled fibers were present in layers II and III. Following bilateral destruction of the olfactory bulb, the density of labeled puncta in layer Ia decreased. These results suggest that the receptor is present on the terminals of the lateral olfactory tract (LOT). Electron microscopic evaluation of layers Ia and Ib revealed that mGluR4a was localized in synaptic terminals in layers Ia and Ib. The terminals had clear, round synaptic vesicles and terminated on asymmetric synapses on dendritic spines and shafts. There was also immunolabeling of some dendritic profiles in layers Ia and Ib that were postsynaptic to unlabeled presynaptic terminals. These observations suggest that mGluR4a is present on presynaptic terminals in the layers of the piriform cortex that receive LOT and associational synapses. This is the same area in which previous studies have revealed the presence of mGluR7 and mGluR8, suggesting that all three receptors may be colocalized.

Animals↗
PubMed2000

Immunolocalization of the mGluR1b splice variant of the metabotropic glutamate receptor 1 at parallel fiber-Purkinje cell synapses in the rat cerebellar cortex.

Several metabotropic glutamate receptor (mGluR) subtypes have been identified in the cerebellar cortex that are targeted to different compartments in cerebellar cells. In this study, preembedding immunocytochemical methods for electron microscopy were used to investigate the subcellular distribution of the mGluR1b splice variant in the rat cerebellar cortex. Dendritic spines of Purkinje cells receiving parallel fiber synaptic terminals were immunoreactive for mGluR1b. With a preembedding immunogold method, approximately 25% of the mGluR1b immunolabeling was observed perisynaptically within 60 nm from the edge of the postsynaptic densities. Values of extrasynaptic gold particles beyond the first 60 nm were maintained at between 10 and 18% along the whole intracellular surface of the dendritic spine membranes of Purkinje cells. For comparison, the distribution of mGluR1a was studied. A predominant (approximately 37%) perisynaptic localization of mGluR1a was seen in dendritic spines of Purkinje cells, dropping the extrasynaptic labeling to 15% in the 60-120-nm bin from the edge of the postsynaptic specialization. Our results reveal that mGluR1b and mGluR1a are localized to the same subcellular compartments in Purkinje cells but that the densities of the perisynaptic and extrasynaptic pools were different for both isoforms. The compartmentalization of mGluR1b and mGluR1a might serve distinct requirements in cerebellar neurotransmission.

Animals↗
PubMed1999

Developmental expression of the group III metabotropic glutamate receptor mGluR4a in the medial nucleus of the trapezoid body of the rat.

A preembedding immunocytochemical method for light microscopy was used to study the postnatal development of expression of the group III metabotropic glutamate receptor mGluR4a in the medial nucleus of the trapezoid body (MNTB) of the rat. Immunoreactivity for mGluR4a was localized in axonal endings wrapping the principal globular neurons in MNTB, known as calyces of Held. The percentage of calyces of Held immunoreactive for mGluR4a increased progressively from postnatal day 3 (PND3), showing the highest density of labeled calyces by PND9. From this postnatal age on, a gradual reduction in the number of mGluR4a-immunopositive calyces of Held was observed, reaching the lowest level of labeled profiles in adult tissue. The developmental expression of mGluR4a in calyces of Held correlates well with previous studies in young animals showing a modulation of synaptic neurotransmission by group III mGluRs in these giant excitatory synapses made on MNTB principal neurons. All these observations together suggest that the expression of mGluR4a mainly between PND7 and PND12 might be relevant to the maturation and modulation of synaptic transmission at the calyces of Held.

Acoustic Stimulation↗
PubMed1998

Glutamate-like immunoreactivity in ascending spinofugal afferents to the rat periaqueductal grey.

The midbrain periaqueductal gray is a key structure for the mediation of an integrated defence behaviour. Although a prominent role for glutamate in PAG mechanisms is supported by both behavioural and morphological studies, whether PAG afferents conveying somatosensory information constitute a source of glutamatergic input to the PAG remains unknown. Here, we have compared the projection pattern of orthogradely-labelled spinoannular fibres with the distribution of glutamate-like immunoreactivity in the PAG at the light microscopic level. Transaxonal labelling was observed throughout the whole rostrocaudal axis of the PAG except for the dorsolateral regions. Cell-processes and terminal-reminiscent puncta were strongly immunoreactive in all PAG regions, including the dorsolateral areas. To ascertain whether glutamate-immunoreactive puncta observed at light microscopy indeed constituted axon terminals of the spinoannular system, glutamate-like immunoreactivity was assessed in orthogradely-labelled synaptic terminals using a post-embedding immunogold procedure for electron microscopy. Quantitative analysis of gold particle densities revealed over twice as strong an immunoreactivity in anatomically-identified spinoannular axon terminals as in dendrites postsynaptic to them, perikarya and inhibitory Gray II synapses, as well as an over 5-fold heavier immunolabelling than in glial profiles. These findings reveal that glutamate is accumulated in synaptic terminals of the spinoannular system, supporting a neurotransmitter role for this acidic amino acid in spinofugal afferents to the PAG.

Animals↗
PubMed1996

A sparsomycin-resistant mutant of Halobacterium salinarium lacks a modification at nucleotide U2603 in the peptidyl transferase centre of 23 S rRNA.

Sparsomycin, a broad-spectrum antibiotic, acts at the peptidyl transferase centre of the ribosome, stabilizing peptidyl-tRNA binding at the P-site and weakening ternary complex binding. A sparsomycin-resistant mutant was isolated for the archaeon Halobacterium salinarium and shown to lack a post-transcriptional modification of U2603 (Escherichia coli numbering U2584), which is a universally conserved uridine base located within the peptidyl transferase loop of 23 S rRNA. This mutant also exhibited altered sensitivities to the peptidyl transferase antibiotics anisomycin, chloramphenicol and puromycin. Several lines of evidence indicate that the unmodified uridine base lies within the P-substrate site of the peptidyl transferase centre.

Anti-Bacterial Agents↗
PubMed1989

Lipophilic analogues of sparsomycin as strong inhibitors of protein synthesis and tumor growth: a structure-activity relationship study.

Fourteen derivatives of sparsomycin (1) were synthesized. Six of them were prepared following a novel synthetic route starting from the L-amino acid alanine. Some physicochemical properties, viz. lipophilicity and water solubility, of selected derivatives were measured. The biological activity was tested in vitro in cell-free protein synthesis inhibition assays, in bacterial and tumor cell growth inhibition assays, and in the L1210 leukemia in vivo model in mice. Also for selected drugs the acute toxicity in mice was determined. Ribosomes from both an eukaryotic and a prokaryotic organism were used in the protein synthesis inhibition systems. A linear correlation between the lipophilicity parameters measured was observed. Water solubility and drug toxicity in mice were found to be linearly correlated with lipophilicity. All the derivatives studied are more lipophilic than 1. The deshydroxysparsomycin analogues (30-33) showed an interesting phenomenon: increase in hydrophobicity was accompanied by a considerable increase in water solubility. We found that an increase in hydrophobicity of the drug as a result of replacing the SMe group of 1 with larger alkylthio groups causes an increase in the biological activity of the drug. However, not only the hydrophobicity but also shape and size of the substituent are important; in the homologous series 1-9-10-11-12, 21-22-23-24, and 30-31-32-33, highest protein synthesis inhibitory and in vitro cytostatic activity is found with compounds 11, 23, and 32, respectively, and in comparison with the highly active n-butyl compound 10, the isomeric tert-butyl compound 13 is rather inactive. Polar substituents replacing the SMe group, i.e. Cl in 17 and 35, also render the molecule inactive. Substituting the bivalent sulfur atom for a methylene group decreases the drug's activity. This effect can be compensated for by increasing the length of the alkylsulfinyl side chain. The agreement between the results derived from cell-free and "in vivo" tests is good. The assays using ribosomes of bacterial and eukaryotic organisms give similar results although the latter seem to be more sensitive to changes in hydrophobicity of the drug. Our results confirm the presence of a hydrophobic region at the peptidyl transferase center of the ribosome; the interaction of sparsomycin with this region is more pronounced in the eukaryotic particles. The sparsomycin analogues 11, 23, and 30 show the highest antitumor activity against L1210 leukemia in mice, their median T/C values are 386, 330, and 216%, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Structure-activity relationships of sparsomycin: modification at the hydroxyl group.

Ten analogues of the antibiotic sparsomycin were prepared and evaluated in several in vitro tests. Nine of them carry a modification at the hydroxymethylene group of the molecule, two have a disulfide bond instead of the S(O)-CH2-S moiety at the sulfur-containing side chain of the molecule. While the presence of the S-S group decreases the activity of the analogues in all the tests performed, the modification at the OH group has no deleterious effects on the activity when a polyphenylalanine synthesis assay is used in an Escherichia coli extract. The same modifications, however, diminish drastically the activity of the analogues when tested in a similar Saccharomyces cerevisiae extract. A polymerization system in the archaebacterium Halobacterium halobium extract behaves like the eukaryotic preparations. A discrepancy is also found between the results of the polymerization tests and those of the 'puromycin reaction' which is also less sensitive to the modified sparsomycin analogues. The results of cell growth inhibition tests in bacteria as well as in eukaryotic organisms agree only partially with the in vitro data.

Antibiotics, Antineoplastic↗