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Biomedical subjects

S López

Publications and source records attributed to S López.

At least 37 records · Page 2Linked to original sources
PubMed2001

2- and 3-haloalkoxy fischer carbene complexes of chromium as synthons for either hydroxycyclopropanation or oxaspirocyclopropanation of alkenes.

The thermal reaction of 2-haloethoxy- and 3-chloropropoxy(alkenyl)carbene complexes of chromium with electronically neutral alkenes furnished diastereoselectively the corresponding 1-haloalkoxy-l-vinylcyclopropanes that, subjected to subsequent halogen-lithium exchange reactions, provided vinylcyclopropanols or compounds containing the spiro[cyclopropane-tetrahydrofuran/tetrahydropyran] structure, depending on the nature of both the halogen atom and the lithiating reagent. The hydroxycyclopropanation reaction can be efficiently achieved in a one-pot fashion.

Journal Article↗
PubMed2001

Early events of rotavirus infection: the search for the receptor(s).

The entry of rotaviruses into epithelial cells seems to be a multistep process. Infection competition experiments have suggested that at least three different interactions between the virus and cell surface molecules take place during the early events of infection, and glycolipids as well as glycoproteins have been suggested to be primary attachment receptors for rotaviruses. The infectivity of some rotavirus strains depends on the presence of sialic acid on the cell surface, however, it has been shown that this interaction is not essential, and it has been suggested that there exists a neuraminidase-resistant cell surface molecule with which most rotaviruses interact. The comparative characterization of the sialic acid-dependent rotavirus strain RRV (G3P5[3]), its neuraminidase-resistant variant nar3, and the human rotavirus strain Wa (G1P1A[8]) has allowed us to show that alpha 2 beta 1 integrin is used by nar3 as its primary cell attachment site, and by RRV in a second interaction, subsequent to its initial contact with a sialic acid-containing cell receptor. We have also shown that integrin alpha V beta 3 is used by all three rotavirus strains as a co-receptor, subsequent to their initial attachment to the cell. We propose that the functional rotavirus receptor is a complex of several cell molecules most likely immersed in glycosphingolipid-enriched plasma membrane microdomains.

Animals↗
PubMed2001

[Intracranial epidural abscess in a newborn secondary to skin catheter].

Intracranial epidural abscesses are uncommon lesions, being more frequents in older children and adults. They commonly arise as a result of direct extension of a preexisting infection and rarely present with focal deficit. We present a case of a 11-days old preterm infant who developed an intracranial epidural abscess as a result of an infected scalp vein catheter. The diagnosis was made on the basis of the cranial ultrasound and CT scan images. An identified strain of Enterococcus faecium was cultured from all the samples. The patient underwent a right frontal craniotomy with drainage of the abscess and a 2-week total course of intravenous antibiotics was administrated. CT scan imaging 3 week after the procedure demonstrated no evidence of residual lesion. When present, a scalp vein catheter, in absence of others predisponing factors, must be considered as an etiologic agent for an intracranial epidural abscess in this age-group.

Catheterization↗
PubMed2001

Influence of nitrogen source on the fermentation of fibre from barley straw and sugarbeet pulp by ruminal micro-organisms in vitro.

Incubations were carried out with a batch culture system to study the effects of different N sources on the fermentation by ruminal micro-organisms from Merino sheep of two fibre substrates derived from feedstuffs that differed in their fermentation rate. The substrates were neutral-detergent fibre (NDF) from barley straw and sugarbeet pulp. N sources were ammonia (NH4Cl) and peptides (Trypticase). Three treatments were made by replacing ammonia-N with peptide-N at levels of 0 (AMMO), 33 (PEPLOW) and 66 % (PEPHIGH) of total N. There were no differences (P>0.05) between treatments in NDF degradation for both the barley straw and the sugarbeet pulp. Peptides increased (P<0.05) total volatile fatty acids daily production for both substrates, with greater values (P<0.001) for PEPHIGH than for PEPLOW for the sugarbeet pulp. The presence of peptides also increased (P<0.05) microbial N synthesis compared with AMMO, with PEPHIGH supporting more growth (P<0.001) than PEPLOW when the sugarbeet pulp NDF was fermented. The presence of peptides increased (P<0.01) the amount of solids-associated micro-organisms (SAM)-N for both the barley straw and the sugarbeet pulp fibres, values in the PEPHIGH treatment being higher (P<0.001) than those in PEPLOW. The proportion of SAM-N in the total microbial N was not affected (P>0.05) by the presence of peptides compared with the AMMO treatment, but values were greater for the PEPHIGH compared with the PEPLOW N source, reaching statistical significance (P<0.05) only for the sugarbeet pulp. For liquid-associated micro-organisms, the AMMO treatment resulted in the greatest (P<0.05) proportion of N derived from ammonia for both substrates, with a further decrease (P<0.01) for the PEPHIGH treatment compared with the PEPLOW for the sugarbeet pulp, indicating preferential uptake of peptides when they were available. Microbial growth efficiency (g microbial N/kg NDF degraded) was not affected (P>0.05) by N source. These results indicate that N forms other than ammonia are needed for maximal growth of fibre-digesting ruminal micro-organisms.

Animal Feed↗
PubMed2000

Integrin alpha(v)beta(3) mediates rotavirus cell entry.

Rotavirus strains differ in their need for sialic acid (SA) for initial binding to the cell surface; however, the existence of a postattachment cell receptor, common to most, if not all, rotavirus strains, has been proposed. In the present study, antibodies to the alpha(v) and beta(3) integrin subunits, and the alpha(v)beta(3) ligand, vitronectin, efficiently blocked the infectivity of the SA-dependent rhesus rotavirus RRV, its SA-independent variant nar3, and the neuraminidase-resistant human rotavirus strain Wa. Vitronectin and anti-beta(3) antibodies, however, did not block the binding of virus to cells, indicating that rotaviruses interact with alpha(v)beta(3) at a postbinding step, probably penetration. This interaction was shown to be independent of the tripeptide motif arginine-glycine-aspartic acid present in the natural ligands of this integrin. Transfection of CHO cells with alpha(v)beta(3) genes significantly increased their permissiveness to all three rotavirus strains, and the increment of virus infectivity was reverted by incubation of these cells either with antibodies to beta(3) or with vitronectin. These findings implicate alpha(v)beta(3) integrin as a cellular receptor common to neuraminidase-sensitive and neuraminidase-resistant rotaviruses, and support the hypothesis that this integrin could determine, at least in part, the cellular susceptibility to rotaviruses.

Animals↗
PubMed2000

Integrin alpha2beta1 mediates the cell attachment of the rotavirus neuraminidase-resistant variant nar3.

It was previously reported that integrins alpha2beta1, alpha4beta1, and alphaXbeta2 are involved in rotavirus cell infection. In this work we studied the role of integrin subunits alpha2, alpha4, and beta2 on the attachment of rotaviruses RRV and nar3 to MA104 cells. Integrin alpha2beta1 was found to serve as the binding receptor for the neuraminidase-resistant virus nar3, whereas the neuraminidase-sensitive strain RRV interacted with this integrin at a postattachment step. It was shown that nar3 binds alpha2beta1 through the DGE integrin-recognition motif located in the virus surface protein VP5. Integrin subunits alpha4 and beta2 do not seem to be involved in the initial cell binding of either virus.

Antibodies, Monoclonal↗
PubMed2000

Torquoselectivity in the cationic cyclopentannelation of (2Z)-hexa-2,4,5-trienal acetals.

Inter- and intramolecular trapping experiments and density functional theory ab initio calculations for model systems are consistent with the acid-catalyzed rearrangement of 2-[(1Z)-hexa-1,3,4-trienyl]dioxolanes 1 to tetrahydroalkylidenecyclopenta-1,4-dioxins 4; this involves the electrocyclic ring closure of substituted hydroxypentadienyl carbocations. The reaction, which may be considered a variant of the Nazarov cyclization, occurs much more readily than the standard Nazarov cyclization, proceeding rapidly even at -30 degrees C. B3LYP/6-31G**//HF/6-31G** calculations for models 36, 38 and 40 predict that the two alternative conrotations at the cyclization termini are associated with activation energies differing by 0.55, 0.56 and 1.60 kcalmol(-1), respectively, in favour of the R-outwards rotation. This last value corresponds to an E-41/Z-41 product ratio of >99:1 at -60 degrees C, in consonance with the experimental observation that divinylallene 1a rearranges exclusively to E-4a at temperatures below -30 degrees C. At higher temperatures the torquoselectivity of the reaction 1a-->4a is masked by subsequent isomerization to the Z isomer, the greater stability of which is attributable to steric interaction between the substituent at the exocyclic double bond and the bulky neighbouring tBu group in the E isomer.

Journal Article↗
PubMed2000

Characterization of a monoclonal antibody directed to the surface of MA104 cells that blocks the infectivity of rotaviruses.

Rhesus rotavirus (RRV) binds to sialic acid residues on the surface of target cells, and treatment of these cells with neuraminidase greatly reduces virus binding with the consequent reduction of infectivity. Variants that can efficiently infect neuraminidase-treated cells have been isolated, indicating that attachment to sialic acid is not an essential step for animal rotaviruses to infect cells. To identify and characterize the neuraminidase-resistant receptor for rotaviruses, we have isolated a hybridoma that secrets a monoclonal antibody (MAb) (2D9) that specifically blocks the infectivity of wild-type (wt) RRV and of its sialic acid-independent variant nar3, in untreated as well as in neuraminidase-treated cells. The infectivity of a human rotavirus was also inhibited, although to a lesser extent. MAb 2D9 blocks the binding of the variant to MA104 cells, while not affecting the binding of wt RRV; in addition, this MAb blocked the attachment of a recombinant glutathione S-transferase (GST)-VP5 fusion protein, but did not affect the binding of GST-VP8. Altogether these results suggest that MAb 2D9 is directed to the neuraminidase-resistant receptor. This receptor seems to mediate the direct attachment of the variant to the cell, through VP5, while the receptor is used by wt RRV for a secondary interaction, after its initial binding to sialic acid, through VP8. MAb 2D9 interacts specifically with the cell surface by indirect immunofluorescence, immunoelectron microscopy, and FACS. By a solid-phase immunoisolation technique, MAb 2D9 was found to react with three proteins of ca. 47, 55, and 220 kDa, which might form a complex.

Animals↗
PubMed2000

The Effect of Adsorbed Sodium Dodecylsulfate at the Alumina-Water Interface on the Luminescence Quenching of Tris(2,2'-bipyridine) ruthenium(II) by Nitrophenols.

The luminescence quenching of tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)(3)(2+)) by 2-, 3-, and 4-nitrophenol (NO(2)PhOH) was studied in the absence and presence of aggregates of sodium dodecyl sulfate (SDS) in the bulk solution and in the adsorbed state on alpha-alumina at pH 2. At this pH, the alumina has a superficial excess of positive charge. The uncorrected luminescence spectrum of Ru(bpy)(3)(2+) did not show any spectral shift in alumina suspension in the absence of SDS in relation to the spectrum in aqueous solution at pH 2 (lambda(max)=609 nm). In the presence of 1 g/L alumina and concentrations of SDS between 0.6 and 0.8 mM and the critical micellar concentration (CMC), the surfactant forms surface aggregates-hemimicelles or admicelles. In these surface aggregates, the emission spectrum showed a red shift (lambda(max)=637 nm). At SDS concentrations higher than the CMC, the surfactant forms micelles in the bulk solution and surface aggregates onto alpha-alumina. However, from the spectral shift observed with the increase in SDS concentration, it seems that, at high surfactant concentrations in the bulk, the metallic complex prefers to remain in the micellar instead of in the hemimicellar phases. The emission maximum in micelles was in 627 nm. The Stern-Volmer constants (K(SV)) of luminescence quenching were determined from steady-state emission intensity measurements at the maximum of emission in each case. The luminescence quenching of Ru(bpy)(3)(2+) showed that the NO(2)PhOHs are incorporated into both types of aggregates. On the basis of the K(SV) values as a function of the SDS concentration, the process of luminescence quenching of Ru(bpy)(3)(2+) by these compounds is more efficient in premicelles/micelles than in the surface aggregates onto alpha-alumina. This was observed up to a concentration of 5 mM SDS. These results can be interpreted as an effect of the increase in polarity of the micellar microenvironment on the electron-transfer mechanism for the quenching process. At SDS concentrations higher than 5 mM, the plot of K(SV) vs SDS concentration in the presence of 1 g/L alumina is shifted to higher SDS concentrations in relation to the observed plot in the absence of 1 g/L alumina. This fact can be explained in terms of the surfactant that forms surface aggregates onto alumina which do not contain the metallic complex. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Relative localization of viroplasmic and endoplasmic reticulum-resident rotavirus proteins in infected cells.

Replication of rotaviruses, whose capsid is constituted by three concentric layers of proteins, occurs in large cytoplasmic inclusions, termed viroplasms. Subviral, double-layered particles bud from viroplasms to the adjacent endoplasmic reticulum (ER), where the outermost protein layer, formed by VP4 and VP7, is assembled. To better understand the morphogenetic process of the virus, we analyzed the relative distribution of viroplasmic and ER-resident viral proteins. Using double immunostaining and confocal microscopy we observed an extensive co-localization between the ER proteins NSP4 and VP7, and the cytoplasmic protein VP4. These three proteins were found to be organized mostly as ring-like or semicircular structures in close association with viroplasms, except for VP4 which displayed in addition, a filamentous distribution. The observations reported in this study underscore the highly organized nature of rotavirus morphogenesis.

Antigens, Viral↗
PubMed2000

P-selectin expression and Kupffer cell activation in rat acute pancreatitis.

This work studied the activation of hepatic macrophages during acute pancreatitis and the involvement of these cells in the lung inflammatory response. Pancreatitis was induced in Wistar rats by intraductal administration of 5% sodium taurocholate. Three hours after pancreatitis induction, the degree of pulmonary inflammation, TNF-alpha levels, and P-selectin expression were evaluated. The generation of TNF-alpha by Kupffer cells was also measured. Pancreatitis increases the serum concentration of TNF-alpha, neutrophil infiltration, and P-selectin expression in pancreas and lung. In addition, Kupffer cells generate increased levels of TNF-alpha. When Kupffer cells were inhibited, the increase in serum TNF-alpha levels and the infiltration of neutrophils in the lung were prevented, but P-selectin expression remained unmodified. We conclude that pulmonary inflammation induced by acute pancreatitis is mediated by Kupffer cell activation and that pancreatitis induces the expression of P-selectin on pulmonary endothelial cells but this effect is not mediated by Kupffer cells.

Acute Disease↗
PubMed2000

The C-terminal domain of rotavirus NSP5 is essential for its multimerization, hyperphosphorylation and interaction with NSP6.

Rotavirus NSP5 is a non-structural phosphoprotein with putative autocatalytic kinase activity, and is present in infected cells as various isoforms having molecular masses of 26, 28 and 30-34 kDa. We have previously shown that NSP5 forms oligomers and interacts with NSP6 in yeast cells. Here we have mapped the domains of NSP5 responsible for these associations. Deletion mutants of the rotavirus YM NSP5 were constructed and assayed for their ability to interact with full-length NSP5 and NSP6 using the yeast two-hybrid assay. The homomultimerization domain was mapped to the 20 C-terminal aa of the protein, which have a predicted alpha-helical structure. A deletion mutant lacking the 10 C-terminal aa (DeltaC10) failed to multimerize both in yeast cells and in an in vitro affinity assay. When transiently expressed in MA104 cells, NSP5 became hyperphosphorylated (30-34 kDa isoforms). In contrast, the DeltaC10 mutant produced forms equivalent to the 26 and 28 kDa species, but was poorly hyperphosphorylated, suggesting that multimerization is important for this proposed activity of the protein. The interaction domain with NSP6 was found to be present in the 35 C-terminal aa of NSP5, overlapping the multimerization domain of the protein, and suggesting that NSP6 might have a regulatory role in the self-association of NSP5. NSP6 was also found to interact with wild-type NSP5, but not with its mutant DeltaC10, in cells transiently transfected with plasmids encoding these proteins, confirming the relevance of the 10 C-terminal aa for the formation of the heterocomplex.

Animals↗
PubMed2000

Critical role of neutrophils in eliminating Listeria monocytogenes from the central nervous system during experimental murine listeriosis.

Neutrophils are the main inflammatory cell present in lesions involving the central nervous system (CNS) during human and murine listeriosis. In this study, administration of the neutrophil-depleting monoclonal antibody RB6-8C5 during experimental murine listeriosis facilitated the multiplication of Listeria monocytogenes in the CNS. These data suggest that neutrophils play a key role in eliminating bacteria that gain access to the CNS compartment. In addition, we provide evidence that their migration into the CNS may be necessary for the subsequent recruitment of macrophages and activated lymphocytes.

Animals↗
PubMed2000

The VP5 domain of VP4 can mediate attachment of rotaviruses to cells.

Some animal rotaviruses require the presence of sialic acid (SA) on the cell surface to infect the cell. We have isolated variants of rhesus rotavirus (RRV) whose infectivity no longer depends on SA. Both the SA-dependent and -independent interactions of these viruses with the cell are mediated by the virus spike protein VP4, which is cleaved by trypsin into two domains, VP5 and VP8. In this work we have compared the binding characteristics of wild-type RRV and its variant nar3 to MA104 cells. In a direct nonradioactive binding assay, both viruses bound to the cells in a saturable and specific manner. When neutralizing monoclonal antibodies directed to both the VP8 and VP5 domains of VP4 were used to block virus binding, antibodies to VP8 blocked the cell attachment of wild-type RRV but not that of the variant nar3. Conversely, an antibody to VP5 inhibited the binding of nar3 but not that of RRV. These results suggest that while RRV binds to the cell through VP8, the variant does so through the VP5 domain of VP4. This observation was further sustained by the fact that recombinant VP8 and VP5 proteins, produced in bacteria as fusion products with glutathione S-transferase, were found to bind to MA104 cells in a specific and saturable manner and, when preincubated with the cell, were capable of inhibiting the binding of wild-type and variant viruses, respectively. In addition, the VP5 and VP8 recombinant proteins inhibited the infectivity of nar3 and RRV, respectively, confirming the results obtained in the binding assays. Interestingly, when the infectivity assay was performed on neuraminidase-treated cells, the VP5 fusion protein was also found to inhibit the infectivity of RRV, suggesting that RRV could bind to the cell through two sequential steps mediated by the interaction of VP8 and VP5 with SA-containing and SA-independent cell surface receptors, respectively.

Animals↗
PubMed2000

Biochemical characterization of rotavirus receptors in MA104 cells.

We have tested the effect of metabolic inhibitors, membrane cholesterol depletion, and detergent extraction of cell surface molecules on the susceptibility of MA104 cells to infection by rotaviruses. Treatment of cells with tunicamycin, an inhibitor of protein N glycosylation, blocked the infectivity of the SA-dependent rotavirus RRV and its SA-independent variant nar3 by about 50%, while the inhibition of O glycosylation had no effect. The inhibitor of glycolipid biosynthesis d, l-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) blocked the infectivity of RRV, nar3, and the human rotavirus strain Wa by about 70%. Sequestration of cholesterol from the cell membrane with beta-cyclodextrin reduced the infectivity of the three viruses by more than 90%. The involvement of N-glycoproteins, glycolipids, and cholesterol in rotavirus infection suggests that the virus receptor(s) might be forming part of lipid microdomains in the cell membrane. MA104 cells incubated with the nonionic detergent octyl-beta-glucoside (OG) showed a ca. 60% reduction in their ability to bind rotaviruses, the same degree to which they became refractory to infection, suggesting that OG extracts the potential virus receptor(s) from the cell surface. Accordingly, when preincubated with the viruses, the OG extract inhibited the virus infectivity by more than 95%. This inhibition was abolished when the extract was treated with either proteases or heat but not when it was treated with neuraminidase, indicating the protein nature of the inhibitor. Two protein fractions of around 57 and 75 kDa were isolated from the extract, and these fractions were shown to have rotavirus-blocking activity. Also, antibodies to these fractions efficiently inhibited the infectivity of the viruses in untreated as well as in neuraminidase-treated cells. Five individual protein bands of 30, 45, 57, 75, and 110 kDa, which exhibited virus-blocking activity, were finally isolated from the OG extract. These proteins are good candidates to function as rotavirus receptors.

Cholesterol↗
PubMed2000

A generalized Michaelis-Menten equation for the analysis of growth.

The functional form W = (W0Kc + Wf t(c)) /(Kc + t(c)), where W is body size at age t, W0 and Wf are the zero- and infinite-time values of W, respectively, and K and c are constants, is derived. This new generalized Michaelis-Menten-type equation provides a flexible model for animal growth capable of describing sigmoidal and diminishing returns behavior. The parameters of the nonlinear model are open to biological interpretation and can be used to calculate reliable estimates of growth traits, such as maximum or average postnatal growth rates. To evaluate the new model, the derived equation and standard growth functions such as the Gompertz and Richards were used to fit 83 growth data sets of different animal species (fish, mice, hamsters, rats, guinea pigs, rabbits, cats, dogs, broilers, turkeys, sheep, goats, pigs, horses, and cattle) with a large range in body size. A comparative study was carried out based on mathematical, statistical, and biological characteristics of the models. The statistical goodness-of-fit achieved with the new model was similar to that of Richards, and both were slightly superior to the Gompertz. The new model differed from the others with respect to some of the estimated growth traits, but there were highly significant correlation coefficients between estimates obtained with the different models, and the ranking of animals based on growth parameters computed with the new function agreed with the rankings computed by the other models. Therefore, the new model, with its variable inflection point, was able to adequately describe growth in a wide variety of animals, to fit a range of data showing sigmoidal growth patterns, and to provide satisfactory estimates of traits for quantifying the growth characteristics of each type of animal.

Animals↗