PubMed Health⌕ Search

Biomedical subjects

L C Lopez

Publications and source records attributed to L C Lopez.

At least 19 recordsLinked to original sources
PubMed2004

Antiulcerogenic activity of ethanol extract of Solanum variabile (false "jurubeba").

The ethanol extract (EE) of the aerial parts of Solanum variabile Mart. (Solanaceae) was investigated for its ability to prevent ulceration of the gastric and duodenal mucosa at different doses. Its ability to heal chronic ulcer processes was also evaluated. When the HCl/ethanol solution was used to induce gastric ulcer, the EE produced a significant dose-dependent reduction of lesion formation of 51, 74 and 89%, at doses of 250, 500 and 1000 mg/kg, respectively. The 100 mg/kg dose had no significant activity. The EE also significantly reduced the gastric lesions induced by the combination of indomethacin and bethanechol (60 and 72%) at doses of 500 and 1000 mg/kg and also reduced stress-induced gastric ulcer (41%) but only at the doses of 1000 mg/g (P < 0.05). The pylorus-ligature experiment demonstrated that the highest EE dose affected significantly the gastric juice parameters by increasing pH values from 4.08 (negative control) to 5.42 and decreasing acid output from 7.16 (negative control) to 4.26 mEq.mL, 4h. A decrease of gastric contents from 370 mg (negative control) to 240 mg was also observed. The results obtained in the chronic gastric ulcer model indicated that a single oral dose of Solanum variabile (1000 mg/kg) administered for 14 consecutive days accelerated the ulcer healing by 46% compared to a 55% effect of cimetidine. Also, at the dose of 1000 mg/kg, the EE inhibited the onset of duodenal lesions by 64%. The data suggest that the EE of Solanum variabile has a significant preventive, curative and duodenal anti-ulcer effect.

Animals↗
PubMed2002

Genotoxicity of maleic hydrazide, acridine and DEHP in Allium cepa root cells performed by two different laboratories.

The purpose of this paper was to compare the results of the Allium cepa chromosome aberration assay between two laboratories under the same test protocol and at the same time, use chemicals and onions obtained in their own homeland. For this study three chemicals were selected: di(2-ethylhexyl)phthalate (DEHP), maleic hydrazide, and acridine. Both laboratories found genotoxicity with a positive dose-response relationship for maleic hydrazide and acridine. However, for DEHP the results were quite different--one of the laboratories found this compound not genotoxic but the other found a positive response. Although the comparative study was inconclusive for DEHP, it was successful for the maleic hydrazide, acridine and also for the positive control (methyl methanesulfonate). Further studies need to be performed in the case of DEPH.

Acridines↗
PubMed2001

A synthetic strategy leading to monodisperse PPV oligomers by coupling reactions of vinyltrimethylsilanes.

A novel strategy for the synthesis of well-defined oligo(phenylenevinylene)s was developed. The procedure is entirely based upon two coupling processes, both involving vinyltrimethylsilanes. Bis(styryl)benzenes 2a-g bearing two octyloxy groups in the central aromatic ring and various substituents on the external aromatic rings were prepared in good yield by a regio- and stereoselective coupling reaction of 1 with different arenediazonium tetrafluoroborates. Oligomers with a more extended conjugated system, 4a-c, and with m-phenylene subunits 13a,b, were also readily obtained by conversion of the unsaturated trimethylsilyl derivatives 3a,c,d to the corresponding boron derivatives and a subsequent coupling reaction with compounds 2a and 2c.

Journal Article↗
PubMed2001

Factors related to cancer screening in Hispanics: a comparison of the perceptions of Hispanic community members, health care providers, and representatives of organizations that serve Hispanics.

Hispanics have lower rates of screening for cervical, breast, and colon cancer than non-Hispanics. Activities to increase cancer screening in this population may not be informed by Hispanics, which may have implications for success rates of interventions. In this study, the perceptions about cancer screening behaviors in Hispanics are compared among three groups: a random sample of respondents (75% Hispanic) to a population-based survey, health care providers (primarily non-Hispanic), and representatives of organizations that serve Hispanics (36% Hispanic). While there was agreement that socioeconomic factors were important for cancer screening, differing views were expressed regarding the importance of cultural factors for cancer screening among Hispanics. Interventions developed by those who serve the Hispanic population may be based on inaccurate perceptions about the beliefs and practices of the population served. For effective interventions, it will be necessary to understand the factors important to Hispanics for cancer screening.

Adult↗
PubMed1995

Use of smokeless tobacco by Mexican-American high school students.

A survey of 208 girls and 191 boys attending a public high school in southwestern New Mexico was conducted to examine students' use of smokeless tobacco products. One Mexican-American girl identified herself as a user of chewing tobacco. Of the boys 8% (17) indicated that they used chewing tobacco and 7% (15) reported that they dipped snuff. 6% (12) indicated use of both snuff and chewing tobacco. The boys included 153 Mexican-Americans of whom 7% used smokeless tobacco and 26 Anglo-Americans of whom 34% were users.

Adolescent↗
PubMed1994

Smokeless tobacco consumption by Mexican-American University students.

A modified version of the Illinois Department of Public Health Smokeless Tobacco Survey was administered to 220 women and 134 men attending a state university in New Mexico. The respondents included 65 male and 83 female Mexican-Americans as well as 118 female and 59 male Anglo-Americans. All Mexican-American women identified themselves as nonusers of smokeless tobacco. Of the Anglo-American women, one indicated that she used snuff, and 3 disclosed that they chewed tobacco. 33% of the Anglo-American men and 18% of the Mexican-American men stated that they used smokeless tobacco products. A chi-squared analysis showed this difference was significant. Implications are discussed.

Adolescent↗
PubMed1994

Smokeless tobacco consumption by Mexican-Americans and Anglo-Americans in southwestern New Mexico.

A telephone survey was conducted to compare the extent of smokeless tobacco consumption by Anglo-Americans and Mexican-Americans. Using systematic random sampling, one out of every 25 phone numbers was selected from the Grant County, New Mexico, telephone directory. Two hundred and ten individuals were interviewed. All of the female respondents, including 46 Mexican-Americans and 81 Anglo-Americans, indicated that they did not use smokeless tobacco. Twenty-five percent of the 51 Anglo-American males and 26% of the 30 Mexican-American males identified themselves as consumers of smokeless tobacco. A chi-square analysis revealed no significance difference between the number of Mexican-Americans and Anglo-Americans among the male self-identified users of smokeless tobacco.

Adolescent↗
PubMed1993

Dominant negative mutation in cell surface beta 1,4-galactosyltransferase inhibits cell-cell and cell-matrix interactions.

In addition to its traditional location within the Golgi complex, beta 1,4-galactosyltransferase (GalTase) is also present on the cell surface, where it is thought to function as a cell adhesion molecule by binding to extracellular oligosaccharide ligands. Recent studies suggest that cells contain two forms of GalTase with distinct cytoplasmic domains. The longer form of GalTase contains a 13-amino acid cytoplasmic extension and is preferentially targeted to the plasma membrane, relative to the shorter GalTase protein that is confined primarily to the Golgi compartment. In this study, we created a dominant negative mutation that interferes with the function of cell surface GalTase by transfecting into cells cDNAs encoding truncated versions of the long form of GalTase containing the complete cytoplasmic and transmembrane domains, but devoid of the catalytic domain. In both F9 embryonal carcinoma cells and Swiss 3T3 fibroblasts, overexpressing the truncated long GalTase (TLGT) protein displaced the endogenous cell surface GalTase from its association with the cytoskeleton, resulting in a loss of intercellular adhesion and cell spreading specifically on matrices that use GalTase as a cell surface receptor. In contrast, overexpressing the analogous truncated short GalTase (TSGT) protein did not affect cell morphology or GalTase activity. In control assays, inducing the TLGT protein had no effect on cell interactions with fibronectin (which is independent of GalTase), or on the cytoskeleton attachment of another matrix receptor (beta 1 integrin), or on overall glycoprotein synthesis, thus eliminating nonspecific effects of the TLGT protein on cellular adhesion and metabolism. These results represent the first molecular manipulation of cell surface GalTase expression and confirm its function as a cell adhesion molecule. These studies further suggest that the cytoskeleton contains a defined, saturable number of binding sites for GalTase, which enables it to function as an adhesion molecule.

3T3 Cells↗
PubMed1992

Smokeless tobacco consumption in Grant County, New Mexico.

A telephone survey was conducted in order to assess the prevalence of smokeless tobacco consumption in Grant County, New Mexico. Systematic random sampling was used, and 1 out of 25 phone numbers were selected from the county telephone directory. One hundred seventy-eight respondents were surveyed. Thirty-three percent of 96 males and 7% of 82 females identified themselves as smokeless tobacco users.

Adult↗
PubMed1991

Evidence for a molecular distinction between Golgi and cell surface forms of beta 1,4-galactosyltransferase.

beta 1,4-Galactosyltransferase (GalTase) is present on the plasma membrane of many cell types in addition to its traditional location within the Golgi compartment. Recently, the GalTase gene has been shown to encode two proteins that are identical throughout their length except that one has an additional 13-amino acid extension in its amino-terminal cytoplasmic domain. We present evidence here suggesting that the longer GalTase protein, containing this unique 13-amino acid peptide, is preferentially targeted to the plasma membrane, and the shorter GalTase protein resides primarily within the Golgi compartment. S1 nuclease protection assays of RNA from a variety of cells and tissues show that the relative abundance of the short and long GalTase mRNAs correlates with GalTase-specific activities in the Golgi and plasma membranes, respectively. Furthermore, transfection of cDNAs encoding either the long or short GalTase protein into F9 embryonal carcinoma cells suggests that the long GalTase protein is preferentially expressed on the cell surface. These results propose a molecular distinction between the Golgi and cell surface forms of GalTase as well as a novel mechanism for targeting glycoproteins to the cell surface.

Amino Acid Sequence↗
PubMed1991

Aggregation of beta-1,4-galactosyltransferase on mouse sperm induces the acrosome reaction.

beta-1,4-Galactosyltransferase (GalTase) is present on the surface of mouse sperm, where it functions during fertilization by binding to oligosaccharide residues in the egg zona pellucida. The specific oligosaccharide substrates for sperm GalTase reside on the glycoprotein ZP3, which possesses both sperm-binding and acrosome reaction-inducing activity. A variety of reagents that perturb sperm GalTase activity inhibit sperm binding to the zona pellucida, including UDP-galactose, N-acetylglucosamine, alpha-lactalbumin, and anti-GalTase Fab fragments. However, none of these reagents are able to cross-link GalTase within the membrane nor are they able to induce the acrosome reaction. On the other hand, intact anti-GalTase IgG blocks sperm-zona binding as well as induces the acrosome reaction. Anti-GalTase IgG induces the acrosome reaction by aggregating GalTase on the sperm plasma membrane, as shown by the inability of anti-Gal-Tase Fab fragments to induce the acrosome reaction unless cross-linked with goat anti-rabbit IgG. These data suggest that zona pellucida oligosaccharides induce the acrosome reaction by clustering GalTase on the sperm surface.

Acetylglucosamine↗
PubMed1989

Cell surface and Golgi pools of beta-1,4-galactosyltransferase are differentially regulated during embryonal carcinoma cell differentiation.

beta-1,4-Galactosyltransferase (GalTase) has two functionally distinct subcellular distributions. In the Golgi apparatus, GalTase participates in the glycosylation of secretory and membrane-bound glycoproteins, whereas on the cell surface it mediates specific aspects of intercellular adhesion. For this study, a murine GalTase clone was obtained by screening a lambda gt10 cDNA library made from F9 embryonal carcinoma cells with a heterologous bovine GalTase cDNA probe. The murine GalTase cDNA probe was used in conjunction with assays of GalTase activity to investigate the expression and distribution of GalTase during differentiation of F9 stem cells into secretory endodermal epithelium. During the initial phase of F9 cell differentiation, GalTase mRNA levels remained relatively constant; however, as differentiation progressed, as assayed by expression of the differentiation-specific marker laminin B1, GalTase mRNA levels and enzyme activity rose dramatically. Furthermore, subcellular fractionation of these cells showed that the increased GalTase levels were specifically associated with the Golgi apparatus, whereas GalTase specific activity on the plasma membrane remained constant. These results show that levels of cell surface and Golgi GalTase change relative to one another during F9 cell differentiation and suggest that these functionally distinct pools of GalTase are independently and differentially regulated.

Blotting, Northern↗
PubMed1988

Comparison of two independent cDNA clones reported to encode beta 1,4 galactosyltransferase.

The identity of cDNA encoding beta 1,4 galactosyltransferase (EC 2.4.1.38) has been controversial, since two independent and unrelated cDNAs have been cloned (GTcDNA-1 and -2), both of which are thought to encode beta 1,4 galactosyltransferase. We have resolved this issue by examining the expression of the corresponding mRNAs in tissues possessing varying levels of galactosyltransferase activity. The expression of GTcDNA-1 parallels the level of galactosyltransferase activity assayed enzymatically, while the expression of GTcDNA-2 is unrelated to the level of enzyme activity, being virtually undetectable in tissues with abundant galactosyltransferase activity. GTcDNA-2, therefore, does not likely encode beta 1,4 galactosyltransferase, but rather, encodes a product that indirectly influences enzyme activity following cellular transfection.

Animals↗
PubMed1987

Redistribution of mouse sperm surface galactosyltransferase after the acrosome reaction.

Gamete recognition in the mouse is mediated by galactosyltransferase (GalTase) on the sperm surface, which binds to its appropriate glycoside substrate in the egg zona pellucida (Lopez, L. C., E. M. Bayna, D. Litoff, N. L. Shaper, J. H. Shaper, and B. D. Shur, 1985, J. Cell Biol., 101:1501-1510). GalTase has been localized by indirect immunofluorescence to the dorsal surface of the anterior sperm head overlying the intact acrosome. Sperm binding to the zona pellucida triggers induction of the acrosome reaction, an exocytotic event that results in vesiculation and release of the outer acrosomal and overlying plasma membranes. Consequently, we examined the fate of sperm surface GalTase after the acrosome reaction. Contrary to our expectations, surface GalTase is not lost during the acrosome reaction despite the loss of its membrane domain. Rather, double-label indirect immunofluorescence assays show that GalTase is redistributed to the lateral surface of the sperm, coincident with the acrosome reaction. This apparent redistribution of GalTase was confirmed by direct enzymatic assays, which show that 90% of sperm GalTase activity is retained during the acrosome reaction. No GalTase activity is detectable on plasma membrane vesicles released during the acrosome reaction. In contrast, removal of plasma membranes by nitrogen cavitation releases GalTase activity from the sperm surface, showing that GalTase redistribution requires a physiological acrosome reaction. The selective redistribution of GalTase to a new membrane domain from one that is lost during the acrosome reaction suggests that GalTase is repositioned for some additional function after initial sperm-zona binding.

Acrosome↗
PubMed1985

Receptor function of mouse sperm surface galactosyltransferase during fertilization.

Past studies from this laboratory have suggested that mouse sperm binding to the egg zona pellucida is mediated by a sperm galactosyltransferase (GalTase), which recognizes and binds to terminal N-acetylglucosamine (GlcNAc) residues in the zona pellucida (Shur, B. D., and N. G. Hall, 1982, J. Cell Biol. 95:567-573; 95:574-579). We now present evidence that directly supports this mechanism for gamete binding. GalTase was purified to homogeneity by sequential affinity-chromatography on GlcNAc-agarose and alpha-lactalbumin-agarose columns. The purified enzyme produced a dose-dependent inhibition of sperm binding to the zona pellucida, relative to controls. To inhibit sperm/zona binding, GalTase had to retain its native conformation, since neither heat-inactivated nor Mn++-deficient GalTase inhibited sperm binding. GalTase inhibition of sperm/zona binding was not due to steric blocking of an adjacent sperm receptor on the zona, since GalTase could be released from the zona pellucida by forced galactosylation with UDPGal, and the resulting galactosylated zona was still incapable of binding sperm. In control experiments, when UDPGal was replaced with the inappropriate sugar nucleotide, UDPglucose, sperm binding to the zona pellucida remained normal after the adsorbed GalTase was washed away. The addition of UDPGal produced a dose-dependent inhibition of sperm/zona binding, and also dissociated preformed sperm/zona adhesions by catalyzing the release of the sperm GalTase from its GlcNAc substrate in the zona pellucida. Under identical conditions, UDP-glucose had no effect on sperm binding to the zona pellucida. The ability of UDPGal to dissociate sperm/zona adhesions was both time- and temperature-dependent. UDPGal produced nearly total inhibition of sperm/zona binding when the zonae pellucidae were first galactosylated to reduce the number of GalTase binding sites. Finally, monospecific anti-GalTase IgG and its Fab fragments produced a dose-dependent inhibition of sperm/zona binding and concomitantly blocked sperm GalTase catalytic activity. Preimmune IgG or anti-mouse brain IgG, which also binds to the sperm surface, had no effect. The sperm GalTase was localized by indirect immunofluorescence to a discrete plasma membrane domain on the dorsal surface of the anterior head overlying the intact acrosome. These results, along with earlier studies, show clearly that sperm GalTase serves as a principal gamete receptor during fertilization.

Acetylglucosaminidase↗
PubMed1984

Evolution of glucagon genes.

Statistical analyses of DNA sequences of the preproglucagon genes from bovine, human, hamster, and anglerfish suggest that a gene duplication creating two anglerfish genes (AF I and II) occurred about 160 Myr ago, long after the separation of fish and mammals. The analyses further suggest that the internal duplication producing the glucagon and glucagon-like peptide II (GLP-II) regions occurred about 1.2 billion years ago, which would indicate that the GLP-II region was present in the ancestral anglerfish sequence but was silenced or deleted before the gene duplication separating AF I and II. The glucagon-like peptide I (GLP-I) was derived from a duplication of the ancestral glucagon region about 800 Myr ago. The rate of synonymous substitution in these genes is approximately 4.3 x 10(-9) substitutions per year per synonymous site. The rate of nonsynonymous substitution in the signal peptide region is about 1.1 x 10(-9) substitutions per year per nonsynonymous site, a high rate comparable to that in the C-peptide region of preproinsulin. The rate of nonsynonymous substitution in the glicentin-related pancreatic polypeptide (GRPP) region is 0.63 x 10(-9) for the comparisons between mammalian species and 1.8 x 10(-9) for the comparisons between fish and mammals; the moderate rate in mammals suggests a physiological role for GRPP. The glucagon region is extremely conservative; no nonsynonymous substitution is observed in the mammalian genes, and a nonsynonymous rate of 0.18 x 10(-9) was obtained from the comparisons between fish and mammals. In the GLP-I region, the rate of nonsynonymous substitution was estimated to be 0.08 x 10(-9) for the comparisons between mammalian species and 0.30 x 10(-9) for the comparisons between fish and mammals. In the GLP-II region, the rate was estimated to be 0.25 x 10(-9) for the comparisons between mammalian species. Thus, GLP-I and II are also very conservative, which suggests an important physiological role for these peptides.

Animals↗