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Biomedical subjects

A Alvarez

Publications and source records attributed to A Alvarez.

At least 181 records · Page 10Linked to original sources
PubMed1996

p21ras induced differentiation-related gene expression in fetal brown adipocyte primary cells and cell lines.

Transfection of primary rat fetal brown adipocytes with constructs of SV40 large T antigen, alone and together with lys12-mutated H-ras gene, gave permanent cell lines showing an immortalized or transformed phenotype, respectively, all of them selected by the expression of the uncoupling protein (UCP), a tissue-specific marker. Primary brown adipocytes and immortalized cell lines respond to insulin-like growth factor I (IGF-I) by increasing their lipid content and the mRNA expression of both the adipogenic marker fatty acid synthase (FAS) and the thermogenic marker UCP. IGF-I-induced differentiation-related gene expression at 24 h in both primary and immortalized brown adipocytes was mediated by an increase in p21ras.GTP active protein content. Transformed cell lines overexpressing exogenous p21ras (mainly in its ras.GTP active form) constitutively showed a higher lipid content and a higher FAS and UCP mRNA expression compared to primary and immortalized cells. These transformed cells were IGF-I independent with respect to their studied differentiation-related parameters. Additionally, transient transfection of primary brown adipocytes with the transforming ras gene induced UCP and FAS mRNA expression as well as cotransactivated UCP-chloramphenicol acetyltransferase fusion gene. Moreover, IGF-I transactivation of UCP promoter was partially precluded by cotransfection with the dominant-negative ras gene. Our results strongly suggest that IGF-I/p21ras induces adipogenic- and thermogenic-related gene expression in brown adipocytes.

Adipocytes↗
PubMed1996

Presence of laminin and 67KDa laminin-receptor on endothelial surface of lung capillaries. An immunocytochemical study.

The existence of cell surface-associated molecules has been claimed to play a major role in cellular recognition and interaction. In this respect, different tumor cell lines express laminin and its receptor, and this expression has been correlated with metastatic potential. In the present work, we have studied, by electron microscopic immunolabeling methods, the presence of laminin and 67KDa laminin-receptor on the surface of endothelial cells of lung blood capillaries. To label these molecules, we have developed an easy method in which the labeling is carried out "in situ", in previously excised lungs. The presence of both molecules was observed on the luminal surface of endothelial capillaries and, in many cases, gold particles were associated to small open vesicles of the endothelial cells. The results suggest that these molecules, traditionally associated to extracellular matrix, are also expressed in cellular surface of the lung vascular bed.

Animals↗
PubMed1996

Comparison of the biochemical properties, regulation and function of ATP-diphosphohydrolase from human placenta and rat kidney.

ATP-diphosphohydrolase (apyrase. EC 3.6.1.5) has both ATPase and ADPase activity that are stimulated by bivalent metals, with Ca2+ being the most effective. The possible physiological function of this enzyme, associated with placental and renal microvilli, is related to the extracellular metabolism of nucleotides. A comparison of the biochemical properties of human placenta and rat kidney apyrase is presented, showing similarities in Mr. bivalent metal stimulation, nucleotide nonspecificity, insensitivity towards specific ATPase inhibitors, and lack of essential sulfhydryl and aliphatic hydroxyl groups. We describe the treatment of membrane preparations from both tissues with different detergents and the isoelectric focusing of the solubilized proteins to partially purify apyrase. An ectoenzyme localization is assigned both in microvillus membranes and in the vasculature on the basis of organ perfusion experiments with nucleotides in the presence of antibodies. Placental and kidney microvillus membranes inhibited ADP-induced platelet aggregation, in agreement with an extracellular role. Initial studies on enzyme regulation suggested the existence of at least two types of modulatory proteins: an activating protein in the cytosol of both tissues, and an inhibitory protein associated with placental microsomes. Possible hormonal regulation was investigated in kidneys using in vivo estradiol treatment, but only slight changes in total apyrase activity were observed.

Animals↗
PubMed1995

Acetylcholinesterase, a senile plaque component, affects the fibrillogenesis of amyloid-beta-peptides.

Acetylcholinesterase (AChE) colocalizes with amyloid-beta peptide (A beta) deposits present in the brain of Alzheimer's patients. Recent studies showed that A beta 1-40 can adopt two different conformational states in solution (an amyloidogenic conformer, A beta ac, and a non-amyloidogenic conformer, A beta nac) which have distinct abilities to form amyloid fibrils. We report here that AChE binds A beta nac and accelerates amyloid formation by the same peptide. No such effect was observed with A beta ac, the amyloidogenic conformer, suggesting that AChE acts as a 'pathological chaperone' inducing a conformational transition from A beta nac into A beta ac in vitro.

Acetylcholinesterase↗
PubMed1995

Differentiation of rat brown adipocytes during late foetal development: role of insulin-like growth factor I.

Rat brown adipocytes at day 22 of foetal development showed greater size, higher mitochondria content and larger amounts of lipids, as determined by flow cytometry, than 20-day foetal cells. Simultaneously, an inhibition on the percentage of brown adipocytes into S+G2/M phases of the cell cycle was observed between days 20 and 22 of foetal development. The expression of several adipogenesis-related genes, such as fatty acid synthase, malic enzyme, glucose-6-phosphate dehydrogenase and insulin-regulated glucose transporter, increased at the end of foetal life in brown adipose tissue. In addition, the lipogenic enzyme activities and the lipogenic flux increased during late foetal development, resulting in mature brown adipocytes showing a multilocular fat droplet phenotype. Concurrently, brown adipocytes induced the expression of the uncoupling protein (UP) mRNA and UP protein, as visualized by immunofluorescence. The three isoforms of CCAAT enhancer-binding proteins (C/EBPs) were expressed at the mRNA level in brown adipose tissue at day 20. C/EBP alpha decreased and C/EBP beta and delta increased their expression between days 20 and 22 of foetal development, respectively. Brown adipose tissue constitutively expressed insulin-like growth factor I (IGF-I) and IGF-I receptor (IGF-IR) mRNAs. Moreover, IGF-IR mRNA content increased between days 20 and 22 in parallel with the occurrence of tissue differentiation.

Adipocytes↗
PubMed1995

Molecular patterns and sequence polymorphisms in the red and green visual pigment genes of Japanese men.

The red-green pigment gene arrays of 203 (101 from a previous study and 102 from this study) randomly selected men of Japanese ancestry from the Seattle area were screened for the abnormal molecular patterns (deletions and red/green or green/red hybrid genes) that are usually associated with defective color vision. Such molecular patterns were found in approximately 5% of these individuals, which is equivalent to the frequency of phenotypic color vision defects in Japanese males in Japan. Thus, the majority of hybrid genes carried by Japanese males appear to be associated with defective color vision. In contrast, the frequency of hybrid genes among Caucasians and African-Americans is approximately two and five times the frequency of color vision defects in these two ethnic groups, respectively. The coding sequences of 50 males of Japanese ancestry were determined. All the polymorphisms in the red and green pigment genes that were detected in the Japanese sample had been observed in Caucasians and African-Americans. The same polymorphisms of the red pigment gene were present in the green pigment gene, suggesting that gene conversion contributes to sequence homogenization between these pigment genes. As is the case for Caucasians, exon 3 of the red and green pigment genes was observed to be a hot spot for recombination and gene conversion. Fewer polymorphic sites (4 vs 11) and haplotypes (5 vs 14) of the red pigment gene were observed in Japanese than in Caucasians. The Japanese population was more uniform with respect to the red pigment gene, with 70% of individuals having the same haplotype, as compared with the 43% for the Caucasian population. This difference was largely due to the lower degree of polymorphism at position 180 of the red pigment gene in Japanese (84% Ser and 16% Ala vs 62% Ser and 38% Ala.) The number of polymorphic sites and haplotypes in the green pigment gene was similar in the two populations. Nevertheless, the Japanese population was more uniform with 65% having the same haplotype. The difference in the frequency of alleles at position 283 accounted for this difference in haplotype distribution.

Amino Acid Sequence↗
PubMed1995

Early cystic thoracic cord cavity complicating decompressive surgery for spondylotic spinal canal stenosis. Case report.

This is a report of a patient who developed thoracic cystic myelopathy immediately following an otherwise successful decompression operation for spondylotic stenosis secondary to osteophyte formation of the thoracic spinal canal. As this case shows, thoracic laminectomy is not without risks, and cystic myelopathy is a potential complication that should be borne in mind when surgery for spondylosis is being planned. Cavitation of the spinal cord may be associated with trauma secondary to extramedullary cord compression.

Humans↗
PubMed1995

Relationship between antioxidant systems, intracellular thiols and DNA ploidy in liver of rats during experimental cirrhogenesis.

Hyperplastic nodular cirrhosis was induced in rats by long-term (6 month) i.p. administration of thioacetamide at doses of 2.66 mmol/kg body wt, three times per week. The survival rate of animals at the end of the treatment was 90%. To follow the temporal changes samples at 0, 7, 15, 30, 45, 60, 90, 150 and 180 days from rats during thioacetamide intoxication and from chronological controls were obtained. The cirrhogenic ability of this treatment was assessed on the basis of morphological changes: the development of macronodular cirrhosis and the appearance of fibrous septa of collagen through portal spaces. Parameters of liver injury and cholestasis were obtained by assaying the serum activities of isocitrate dehydrogenase and gamma-glutamyltransferase. Enzymes and metabolites related to glutathione redox systems, as well as other antioxidant enzymes, were tested. Catalase and glutathione peroxidase, the two enzymes involved in the elimination of peroxides, and glutathione reductase decreased significantly at the end of the 6 months of intoxication, while Cu-Zn and Mn superoxide dismutases increased progressively during the long-term thioacetamide treatment. Protein thiol levels profile showed a biphasic change increasing from the 7th day and were insensitive to the 30% depletion of intracellular glutathione (GSH). To study the relationship of the intracellular thiols on the mechanisms of cell proliferation and differentiation during the cirrhogenic process, DNA content was assayed by flow cytometry in isolated hepatocytes, and DNA ploidy and distribution between G0-G1, S and G2 + M phases were determined. Remarkable changes in relation to a sharp increase in diploid population from 7 to 180 days (24.5%-->85.5%), a pronounced decrease in polyploid populations (tetraploid+octoploid) in the same period (73.7%-->12.3%), and elevations in the populations in S phase (S1 + S2) were observed in thioacetamide-treated rats. The results obtained indicate that hepatocytes isolated from thioacetamide-treated rats showed a marked tendency to diploidy, an enhancement in DNA replication parallel to the hepatic content of protein sulphydryl groups and a significant decline in antioxidant enzyme activities. The increase in protein thiols was independent of GSH level and of the thiol redox state.

Animals↗
PubMed1995

Enhanced intracellular calcium concentration during poliovirus infection.

The infection of human fibroblasts by poliovirus leads to a notable increase in the intracellular calcium concentration, [Ca2+]i, measured by microfluorimetry or by flow cytometry. [Ca2+]i increases from 2 to 3 h postinfection, and by the fifth hour there is a 5- to 10-fold increase in [Ca2+]i. At this time postinfection there is active viral protein synthesis. The modifications in [Ca2+]i are not observed in the presence of cycloheximide, guanidine, or Ro 09-0179, indicating that virus gene expression is required for the increase in [Ca2+]i. Attempts to identify the source of the intracellular Ca2+ by using different inhibitors of calcium fluxes suggest that calcium enters from the culture medium through voltage-sensitive calcium channels.

Calcium↗
PubMed1995

Splenic B lymphocyte programmed cell death is prevented by nitric oxide release through mechanisms involving sustained Bcl-2 levels.

Incubation of ex vivo cultured mature B cells in the presence of nitric oxide or nitric oxide-donor substances delays programmed cell death as determined by the appearance of DNA laddering in agarose gel electrophoresis or by flow-cytometry analysis of DNA. Nitric oxide also rescues B cells from antigen-induced apoptosis but fails to provide a co-stimulatory signal that converts the signal elicited by the antigen into a proliferative response. The protective effects of nitric oxide against programmed cell death can be reproduced by treatment of the cells with permeant analogues of cyclic GMP. Regarding the mechanisms by which nitric oxide prevents apoptosis in B cells, we have observed that nitric oxide release prevents the drop in the expression of the protooncogene bcl-2, both at the mRNA and protein levels, suggesting the existence of an unknown pathway that links nitric oxide signaling with Bcl-2 expression.

Animals↗
PubMed1995

Cyclic AMP modulates the rate of 'constitutive' exocytosis of apical membrane proteins in Madin-Darby canine kidney cells.

Madin-Darby canine kidney and other epithelial cell lines (e.g. Caco-2, MCF-10A and MCF-7) develop intracellular vacuoles composed of apical membrane displaying microvilli (VACs) when impaired from forming normal cell-to-cell contacts. In a previous publication, we showed that VACs are rapidly exocytosed upon treatment with 8-Br-3',5'-cyclic adenosine monophosphate (8-Br-cAMP), a membrane-permeable analog of cAMP, and that this exocytosis correlates with variations in the cellular cAMP concentration in response to the cell-cell contacts. In the present work, we tested the hypothesis that cAMP may be a positive modulator of the 'constitutive' exocytic pathway. To mimic conditions in cells with incomplete intercellular contacts, the intracellular levels of cAMP were decreased by means of two independent approaches: (i) pores were induced in the plasma membrane with the polypeptidic antibiotic subtilin, thus allowing small molecules (including cAMP) to permeate and move out of the cytoplasm; and (ii) adenylate cyclase and protein kinase A were blocked with specific inhibitors. In all cases, the intracellular levels of cAMP were measured and, in porated cells, equilibrated to simulate the corresponding physiological intracellular concentrations. The decrease in cAMP within the physiological range resulted in a decreased rate of transport of an apical marker of the constitutive pathway (influenza virus hemagglutinin) from the trans-Golgi network to the apical plasma membrane. Likewise, the delivery of a number of cellular apical proteins to the plasma membrane was retarded at low cAMP concentrations. The inhibitors of adenylate cyclase failed to block basolateral delivery of vesicular stomatitis virus G protein. This differential modulatory effect may represent a differentiation-dependent control of the insertion of apical membrane in epithelial cells.

8-Bromo Cyclic Adenosine Monophosphate↗