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S Estrada

Publications and source records attributed to S Estrada.

At least 37 records · Page 2Linked to original sources
PubMed1997

Smooth muscle relaxing flavonoids and terpenoids from Conyza filaginoides.

Activity-guided fractionation of the smooth muscle relaxing, chloroform-methanol (1:1) extract of Conyza filaginoides (D.C.) Hieron (Asteraceae) led to the isolation of three flavonoids (quercetin 3-glucoside, rutin, and pinostrobin), one sterol (alpha-spinasterol), a sesquiterpenoid (beta-caryophyllene 4,5-alpha-oxide), and two triterpenoids (erythrodiol and 3-beta-tridecanoyloxy-28-hydroxyolean-12-ene). 3-beta-Tridecanoyloxy-28-hydroxy-olean-12-ene is a new naturally occurring terpenoid. All the isolated compounds induced a concentration-dependent inhibition of the spontaneous contractions of rat ileum. The spasmolytic activity exhibited by the extract and active principles tends to support the traditional use of C filaginoides as an antispasmodic agent.

Animals↗
PubMed1996

Cathepsins D, B, and L in transformed human breast epithelial cells.

To investigate the regulation of lysosomal enzymes during carcinogenesis, we measured cathepsins (Cats) D, B, and L in MCF-10F, which is a human breast epithelial cell line, and cells evolved after treatment with carcinogen and transfected with c-Ha-ras oncogene. The clones used in this study, MCF-10FTras, D3, D3-1, and D3-1Tras, expressed no estrogen receptors and gradually increased invasive potential, while oncogene-transfected lines were also tumorigenic in SCID mice [16, 19]. Cats D, B, and L were determined in the cells and in cell media using enzyme-linked immunosorbent assay (ELISA), specific enzyme activity measurements, and immunocytochemistry. The major intra- and extracellular lysosomal proteinase in these cells was Cat D (30-180 pm/mg), followed by Cat B (2-10 pm/mg) and Cat L (1-5 pm/mg). An inverse relationship between intracellular Cat D levels and invasive potential of carcinogen-treated and c-Ha-ras oncogene-transfected cell lines was observed. No significant changes in extracellular concentration of Cat D precursor in this series of cell lines was observed. Intracellular levels of Cats B and L were unchanged or slightly lower in carcinogen-treated D3 and D3-1 cells, as well as in MCF-10FTras. On the other hand, in D3-1Tras cell line, evolving from c-Ha-ras transfected D3-1 line, 3.5 fold and 4.4 fold increases in Cat B and Cat L, respectively, but a 2 fold decrease in Cat D, were observed compared to the parental cell line. Immunocytochemical staining showed a granular, polarized perinuclear and cytoplasmic staining of cathepsins in all cell lines. Cysteine proteinases stained more frequently and more intensely in D3-1Tras compared to other lines, confirming the immunochemical assays. We hypothesize that several molecular events, caused by a carcinogen and an oncogene such as c-Ha-ras, are needed to increase Cat B and Cat L, but not Cat D, expression. Therefore, the cysteine and aspartic lysosomal proteinases are differentially expressed in the breast cell lines with more invasive phenotype.

Breast↗
PubMed1995

Characterization by spectroscopic, kinetic and equilibrium methods of the interaction between recombinant human cystatin A (stefin A) and cysteine proteinases.

The near-UV spectroscopic changes induced by the binding of recombinant human cystatin A to papain were appreciably different from those induced by cystatin C, reflecting mainly interactions involving the single tryptophan of cystatin C, Trp-106. Cystatin A bound tightly and rapidly to papain and cathepsin L, with dissociation equilibrium constants of approximately 10(-11)-10(-13) M and association rate constants of 3 x 10(6)-5 x 10(6) M-1.s-1. These affinities are at least 50-100-fold higher than previously reported values. The kinetics of binding to papain were consistent with a simple reversible bimolecular reaction mechanism, indicating that cystatin A, like chicken cystatin and cystatin C, binds to papain with no appreciable conformational adaptation of either reacting protein. Cystatin A bound more weakly to actinidin and cathepsins B, C and H, with dissociation equilibrium constants of 10(-8)-10(-9) M. The weaker binding to cathepsin B was largely due to a considerably reduced association rate constant (approximately 4 x 10(4) M-1.s-1), consistent with the 'occluding loop' of cathepsin B markedly restricting the access of cystatin A to the active site. The lower affinities for actinidin and cathepsins C and H were due partly to lower association rate constants (2 x 10(5)-6 x 10(5) M-1.s-1) but primarily to higher dissociation rate constants. The mode of binding of cystatin A to inactivated papains indicated that there is appreciably less space around the active-site cysteine of papain in the complex with cystatin A than in the complexes with chicken cystatin and cystatin C. An N-terminally truncated form of cystatin A, lacking the first six residues, had considerably lower affinity for papain than the full-length inhibitor, consistent with an intact N-terminal region being of importance for proteinase binding.

Amino Acid Sequence↗
PubMed1994

Hormone receptors and cathepsin D levels in human breast epithelial cells transformed by chemical carcinogens and c-Ha-ras transfection.

The objective of this work was to determine whether transformation of the human breast epithelial cell line MCF-10F by the chemical carcinogens 7, 12-dimethylbenz(a)anthracene (DMBA) or benzo(a)pyrene (BP), or c-Ha-ras oncogene transfection, influence the expression of epidermal growth factor receptor (EGFR), estrogen (ER) or progesterone (PR) receptors, and the content of cathepsin-D (Cath.D). MCF-10F control cells did not express any of the phenotypes of neoplastic transformation, whereas carcinogen-treated cells and clones derived from the latter formed colonies in agar-methocel, and exhibited increased chemotaxis and chemoinvasion. Clone BP-1E was also tumorigenic in SCID mice. The BP1 cell line transfected with mutated c-Ha-ras oncogene, named BP1-Tras, became more aggressive after transfection and decreased the latency time to tumorigenesis. Radioligand binding and immunocytochemical reactions were utilized for determining the receptors and Cath.D content of control and carcinogen-treated cells and their derived clones. MCF-10F cells contained 37 fmol/mg of protein of EGFR, ER and PR were undetectable, and Cath.D content was 70 fmol/mg protein. EGFR content was significantly higher in D3-1 and BP1-E cell lines vs the control MCF-10F and the other DMBA and BP clones, correlating positively with the emergence of the transformation phenotype. Whereas EGFR levels were not significantly different in BP1-Tras cells when compared with BP1-E, the former were more tumorigenic in SCID mice, an observation suggesting an alternative pathway in these cells in the formation of tumors.(ABSTRACT TRUNCATED AT 250 WORDS)

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1992

Nigericin forms highly stable complexes with lithium and cesium.

Nigericin is a monocarboxylic polyether molecule described as a mobile K+ ionophore unable to transport Li+ and Cs+ across natural or artificial membranes. This paper shows that the ion carrier molecule forms complexes of equivalent energy demands with Li+, Cs+, Na+, Rb+, and K+. This is in accordance with the similar values of the complex stability constants obtained from nigericin with the five alkali metal cations assayed. On the other hand, nigericin-alkali metal cation binding isotherms show faster rates for Li+ and Cs+ than for Na+, K+, and Rb+, in conditions where the carboxylic proton does not dissociate. Furthermore, proton NMR spectra of nigericin-Li+ and nigericin-Cs+ complexes show wide broadenings, suggesting strong cation interaction with the ionophore; in contrast, the complexes with Na+, K+, and Rb+ show only clear-cut chemical shifts. These latter results support the view that nigericin forms highly stable complexes with Li+ and Cs+ and contribute to the explanation for the inability of this ionophore to transport the former cations in conditions where it catalyzes a fast transport of K+ greater than Rb+ greater than Na+.

Biological Transport↗
PubMed1987

Formation of ion-translocating oligomers by nigericin.

At pH 4.0, greater than 10(-7) M nigericin was found capable of conducting net charge transfer across bimolecular lecithin membranes, with a stoichiometry of three uncharged ionophore moieties per cation. At neutral or alkaline pH, nigericin catalyzed the transfer of net charge through dimer forms. In agreement with these results, quantitative analysis of nigericin-potassium complexes formed at pH 4.0 showed a 3:1 ratio, and a 2:1 ratio at neutral or alkaline pH. A 1:1 stoichiometry was observed when the ionophore complex was not transferred from methanol-water to chloroform. Moreover, 1H-NMR spectra of nigericin-cation complexes formed at pH 4.0, displayed clear-cut chemical shift variations different to those observed at neutral or alkaline pH. Thus, it is apparent that acid pH causes a transition from dimeric to trimeric forms of nigericin-cation complexes. The membrane conductance increased up to ten times when negatively charged phosphatidyl glycerol was used, while the conductance decreased in positively charged cetylpyridinium containing membranes at pH 4.0. These results suggest that the nigericin-K+ oligomeric complex is positively charged. In this respect, pKa values around 8.0 were obtained for the nigericin carboxylate group in media of different dielectric constant, indicating that this chemical group is undissociated under these conditions. Moreover, the values for the complex formation constants as well as the delta G values calculated for the dimers and trimers indicated that such ionophore cation oligomeric complexes are thermodynamically stable.

Anti-Bacterial Agents↗
PubMed1987

Mechanism of ammonium translocation in rat liver mitochondria. Finger-printing of the translocator.

We have studied whether ammonia crosses the cristae membrane of rat liver mitochondria as a charged (NH4+) or an uncharged (NH3) species. Passive swelling of mitochondria suspended in ammonium and/or sodium acetates showed that: swelling depends upon ammonium concentration in the same way it depends on sodium (at constant acetate concentration). The curves reach a plateau at 115 mM ammonium and 100 mM sodium. A two units change of pH induces a two orders of magnitude change in the concentration of NH3, while NH4+ remains almost constant. However, the extent and initial rates of swelling are not significantly modified. The results are discussed as ammonia being translocated as a charged species via a transport system. The transport system was characterized studying the swelling reaction of inhibited rat liver mitochondria suspended in acetate salts of alkali, ammonium and nitrogenous cations: The selectivity pattern of the translocator is: NH4+ greater than Na+ greater than Li+ greater than K+ greater than Rb+ greater than Cs+ (Eisenman's sequence X). For homologous nitrogenous cations permeability decreases as molecular weight increases or free solution mobility decreases. Ions with Ladd Radius shorter than 3.7 to 3.8 A and cross sections below 15 A2 are permeable, those with longer radius or larger areas are not. As the chain of monosubstituted nitrogenous cations is lengthened, permeability decreases, passes through a minimum around NC = 4 and then increases. Nitrogenous cations which do not make hydrogen bonds do not enter mitochondria, those with one, two or three donor protons have similar permeabilities, and those with one, two or three oxygen acceptors increase their permeability almost linearly. Formamidine, acetamidine, TEA, guanidine derivatives, N,N-dicyclohexylcarbodiimide and N-ethyl maleimide failed to inhibit sodium-induced mitochondrial passive swelling.

Acetates↗
PubMed1986

Magnesium and octylguanidinium inhibition of monovalent cation translocation in mitochondria.

We have studied the inhibitory effects of several cations (OG+, Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, La3+) on the uniport and exchange pathways for Na+ and K+ of rat liver mitochondria. Swelling of mitochondria suspended in sodium or potassium acetates indicates that: 1. Sodium passive influx to inhibited mitochondria is not affected by OG+ (in the microM range), and mM concentrations of polyvalent cations only induce a poor inhibition, the sequence being: La3+ greater than Mn2+ greater than Ca2+ greater than Mg2+ greater than Sr2+ = 0. 2. Sodium active influx is 50% inhibited by 60 microM Mg2+ or 90 microM OG+. La3+, Mn2+, Ca2+ and Sr2+ also inhibit Na+ influx (mM range). 10 mM Mg2+ or 35 microM OG+ are required to inhibit 50% K+ active influx. 3. Alkali cation efflux from partially swollen inhibited mitochondria is 50% blocked by 2 mM Mg2+ or 105 microM OG+ when sodium is the major permeable cation in the bathing solution. 3 mM Mg2+ or 3.8 microM OG+ are required for 50% inhibition when mitochondria are suspended in potassium acetate. 4. Alkali cation efflux from partially swollen respiring mitochondria suspended in sodium acetate is promoted by concentrations above 0.1-0.2 mM Mg2+ or 50-100 microM OG+. These data fit a mechanism including an energy-dependent Mg2+ and OG+ sensitive inward sodium translocator and a Mg2+ and OG+ insensitive cation/H+ exchanger working in dynamic balance.

Animals↗