Samuel Martín-Sosa - Academia.edu (original) (raw)

Papers by Samuel Martín-Sosa

Anales de la Facultad de Veterinaria de León, 1996

Las evidencias del cambio climatico son cada vez mas abrumadoras. En los ultimos anos estamos asi... more Las evidencias del cambio climatico son cada vez mas abrumadoras. En los ultimos anos estamos asistiendo a cambios sin precedentes a nivel global, y estamos al mismo tiempo comenzando a sufrir de forma directa los embates de este fenomeno.

En los ultimos anos se ha dado un incremento considerable de las noticias sobre cambio climatico ... more En los ultimos anos se ha dado un incremento considerable de las noticias sobre cambio climatico en los medios de comunicacion, especialmente a partir de 2007 (Boykoff et al., 2017). La prensa, en papel impreso o Internet, sigue siendo uno de los canales informativos mas importantes, liderando el apartado de credibilidad de los medios de comunicacion en paises como Francia, Gran Bretana o Italia (Buckley et al. 2017). Sin embargo, la creciente literatura sobre el papel de la prensa en la cobertura del cambio climatico (Brulle et al., 2012) se circunscribe mayoritariamente al analisis de periodicos en un solo pais (Schmidt et al. 2013). Por tanto, y a pesar del largo recorrido de algunos proyectos de investigacion enfocados a varios paises, como el coordinado por el Center for Science and Technology Policy Research de la Universidad de Colorado (Boykoff et al. 2017), parece necesaria una mayor profundizacion en los estudios comparativos para identificar los elementos clave de la difu...

El estudio se estructura en cuatro partes. La primera aborda el contenido de acidos sialicos tota... more El estudio se estructura en cuatro partes. La primera aborda el contenido de acidos sialicos totales y de acidos sialicos unidos a oligosacaridos, glilcoproteinas y caseina a lo largo de la lactacion. Se estudian tambien los tipos de acido sialicos. Seguidamente se analizan los cambios en el contenido de oligosacaridos sialilados a lo largo de la lactacion haciendo una comparacion con la composicion encontrada en la leche de vaca y en formulas infantiles. Se identificaron siete oligosacaridos sialilados en leche humana. Un tercer apartado aborda la capacidad inhibitoria de los oligosacaridos de la leche frente a cepas de Escherichia coli enterotoxigenicas y la responsabilidad de la fraccion sialilada en dicha inhibicion. Por ultimo, se realiza un estudio mas exhaustivo del contenido y de la composicion de los gangliosidos a lo largo de la lactacion y de su contenido en acidos grasos. Finalmente se estudia la capacidad de union de estas moleculas a una cepa enterotoxigenica. A lo lar...

Lipids, 2004

The objectives of this work were to study the FA composition of milk gangliosides, as well as to ... more The objectives of this work were to study the FA composition of milk gangliosides, as well as to gain further insight into the characterization of human milk gangliosides. The potential capacity of human milk gangliosides to adhere to human enterotoxigenic Escherichia coli (ETEC-strains) was also studied. Human milk gangliosides were isolated and identified by high-performance TLC or immunoassay. The latter also was used to assay bacterial adhesion. The FA composition of gangliosides was studied by GC. The presence of O-acetyl GD3 (Neu5,9Ac 2 α2-8 NeuAcα2-3Galβ1-4GlcCer) and trace amounts of GM1 [Galβ1-3GalNAcβ1,-3(NeuAcα2-3)Galβ1-4GlcCer] in human milk was confirmed. Medium-chain FA were almost absent in colostrum, whereas in the subsequent stages they rose to 20%. The levels of long-chain FA decreased after colostrum. With respect to the degree of saturation, gangliosides from colostrum were richer in monounsaturated FA than gangliosides synthesized during the rest of the lactation period, opposite to the pattern for PUFA. A human-ETEC colonization factor antigen II-expressing strain showed binding capacity to human milk GM3 (NeuAcα2-3Galβ1-4GlcCer). New data on human milk gangliosides have been gathered. A thorough knowledge of their composition is needed since they may have important biological implications in regard to newborns' defense against infection.

The Journal of Nutrition, 2002

Milk oligosaccharides can act as soluble receptors that block bacterial adhesion to the different... more Milk oligosaccharides can act as soluble receptors that block bacterial adhesion to the different epithelia. Colonization factor antigens (CFA)/I-and CFA/II-expressing enterotoxigenic Escherichia coli (ETEC) strains constitute one of the main causes of diarrhea in infants. Here, the inhibition of hemagglutination mediated by these strains by milk oligosaccharides was tested. Human milk oligosaccharides showed a strong inhibitory capacity, which decreased when the oligosaccharides were desialylated. Because milk oligosaccharides also are present in the urine of neonates receiving mothers' milk, their ability to bind two uropathogenic Escherichia coli (UPEC) strains was also examined. UPEC strains expressing P (Pap) and P-like (Prs) fimbriae are responsible for infections of the urinary tract such as pyelonephritis and cystitis. The hemagglutination mediated by these strains was inhibited by human milk oligosaccharides. The sialylated fraction was partially responsible for this inhibition in the case of the UPEC expressing the P-like fimbria because differences were found after desialylation. Although bovine milk oligosaccharides were less efficient at inhibiting the hemagglutination of ETEC strains, they were still quite good inhibitors of UPEC strains.

Journal of dairy science, 2001

The sialoglycoconjugate content of human milk has been extensively studied. However, little atten... more The sialoglycoconjugate content of human milk has been extensively studied. However, little attention has been paid to the changes occurring in these compounds in bovine milk during lactation. Since sialoglycoconjugates are very abundant in milk from the early stages of lactation, they have been suggested to be important for the nutrition of the newborn during the first months of life. The distribution of sialoglycoconjugates (expressed as glycoconjugate-bound sialic acid) from four different stages of lactation (colostrum, transitional, mature, and late-lactation milks) was investigated in four Spanish-Brown cows. All the fractions studied (total sialic acids, glycoproteins, oligosaccharides, casein, and gangliosides) showed a similar trend. We found the highest values in the colostrum, these decreasing in transitional and mature milks and increasing again in late-lactation milk. We also found a selective change in the relative contents of glycoprotein- and oligosaccharide-bound si...

Journal of dairy science, 2003

Several lines of research support a role for human milk oligosaccharides in the defense of breast... more Several lines of research support a role for human milk oligosaccharides in the defense of breast-fed infants against pathogens. Some ofthese oligosaccharides contain at least one moiety of sialic acid and are, thus, termed sialyloligosaccharides. These constitute a significant component (>1 g/L) of human milk. It is well established that milk composition varies among species, and previous reports have indicated that one ofthe differences between human and bovine milk is precisely their contents of sialyloligosaccharides. Because most infant formulas are manufactured with bovine milk components, it follows that formula-fed and breast-fed infants ingest dissimilar quantities of these carbohydrate structures. To ascertain these differences and their impact along lactation, the contents of oligosaccharide-bound sialic acids and major sialyloligosaccharides in samples of human and bovine milk (obtained at different lactation stages) were determined. In addition, infant formulas were ...

Lipids, 2001

The stage of lactation is one of the most important factors that influence milk composition. Chan... more The stage of lactation is one of the most important factors that influence milk composition. Changes in fatty acids from triacylglycerols and phospholipids have already been reported. In this study, we looked for a lactational change in the ganglioside lipid moiety since ganglioside contents and patterns vary strongly with stage of lactation. Individual gangliosides from four stages were isolated, methanolyzed to cleave the bonds between individual constituents, and derivatized for gas-liquid chromatography and gas chromatography/mass spectrometry analyses. Ceramide components, both fatty acids (as methyl esters derivatives) and long-chain bases, were identified and quantified. The results pointed to a marked change in ceramide from colostrum to milk that was characterized by a dramatic decrease in saturated and the longest-chain fatty acids as well as an increase in 18:1 and 18:2. The major long-chain base along lactation was a recently described structure, 3-ethoxy-15:0 sphinganine. Other new long-chain base structures appeared in these gangliosides. All these changes suggest differences in the fluidity of the fat globule membrane, reflecting physiological variations in cows with respect to milk production.

Lipids, 2003

Diarrhea caused by enterotoxigenic Escherichia coli (ETEC) is the main infectious disease of newb... more Diarrhea caused by enterotoxigenic Escherichia coli (ETEC) is the main infectious disease of newborn calves. The first step of infection involves bacterial attachment to the intestinal mucosa. This adhesion is mediated by fimbriae that recognize some glycoconjugates on the host cell surface, in particular, several gangliosides. Because milk also contains gangliosides, these have been suggested to serve as ligands for bacterial fimbriae and thus prevent the bacterial attachment to mucosa. The most relevant ETEC strains in calves, including those with K99 and F41 fimbriae, were assayed to determine whether they are able to bind gangliosides isolated from several stages of bovine lactation. Both GM3 and GD3, the main gangliosides of milk, were recognized by ETEC strains, although the different fimbriae showed diverse levels of affinity. Unexpectedly, the adhesion to colostral gangliosides was considerably weaker than that to gangliosides from the other stages of lactation. Because the carbohydrate moiety did not change and because differences in the percentages of unsaturated FA and sphingosine between colostrum and other stages were observed, we conclude that the differences in adhesion could be due to a different composition of the ganglioside ceramide.

Journal of Pediatric Gastroenterology and Nutrition, 2004

Objectives: The protective effect of human milk against infection is well known. Several non-immu... more Objectives: The protective effect of human milk against infection is well known. Several non-immunologic components, including complex carbohydrates, have been described. The present study was undertaken to determine the sialic acid distribution in different milk fractions (complex carbohydrates). Methods: Milk samples from 12 Spanish women at three different lactational stages (colostrum, transitional milk and mature milk) were analyzed. Total and glycoprotein-bound, oligosaccharide-bound, casein-bound, and lipid-bound sialic acids were determined. Results: Sialic acids from human milk are mainly bound to oligosaccharides and only a small amount is present bound to glycoproteins or in the free form. All the fractions analyzed showed a similar trend: sialic acids decrease rapidly along lactation. Casein-bound sialic acid does not follow this trend. We detected the presence of an O-acetylated species of N-acetylneuraminic acid. Conclusions: In human milk from Spanish women we observed slightly different values than those previously reported. This could be a result of population differences but nutritional or methodological aspects can not be discarded.

Estudios sobre el Mensaje Periodístico

A la vez que el consenso sobre el cambio climático se ha ido trasladando del ámbito científico a ... more A la vez que el consenso sobre el cambio climático se ha ido trasladando del ámbito científico a la opinión pública, los argumentos escépticos y negacionistas parecen haberse moderado y adoptan estrategias más sutiles. Sin embargo, pocos trabajos analizan estos discursos a partir de un número relevante de contenidos periodísticos. Este estudio analiza los argumentos escépticos y negacionistas en la prensa española entre 2015 y 2021 con una muestra final de 147 artículos seleccionados a partir de una técnica de búsqueda agregada de conceptos clave en Factiva. Los resultados señalan que el eje argumental es prioritariamente ideológico y que el científico es antes un recurso argumentativo que un eje. Sin embargo, el eje económico dirige principalmente el posicionamiento escéptico sobre las medidas a adoptar ante el cambio climático. Por último, las ideas de verdad y libertad funcionarían como vectores argumentativos del discurso escéptico ante el cambio climático.

Glycoconjugate Journal, 2002

Milk oligosaccharides have been proposed to play an important role in newborn defense, blocking b... more Milk oligosaccharides have been proposed to play an important role in newborn defense, blocking bacterial adhesion to the intestinal mucosa and preventing infections. Some studies have been performed on human milk oligosaccharides. Here we checked whether bovine milk oligosaccharides would achieve the same protective action against the most common calf enteric pathogens. Seven enterotoxigenic Escherichia coli strains, isolated from diarrheic calves, were selected. All strains managed to agglutinate horse erythrocytes, and we therefore used the inhibition of hemagglutination in the presence of oligosaccharides as an indicator of the union between oligosaccharide and bacterial adhesins. Oligosaccharides from different stages of bovine lactation and standard oligosaccharides were assayed. Midlactation milk, in particular that corresponding to the transition period, proved to be the most efficient at inhibiting hemagglutination. The standard oligosaccharides used pointed to the preferen...

espanolSe ha estudiado el contenido de diversos sialoglicoconjugados de la leche de vaca, cabra y... more espanolSe ha estudiado el contenido de diversos sialoglicoconjugados de la leche de vaca, cabra y oveja y su evolucion durante la lactacion. El contenido de acidos sialicos totales y el de acidos sialicos unidos a lipidos (gangliosidos) es alto en el calostro, disminuyendo a medida que avanza la lactacion en las tres especies estudiadas. La leche de cabra presenta un contenido de acidos sialicos totales superior a las de vaca y oveja en cualquier fase de la lactacion, mientras que la leche de vaca tiene practicamente 10 veces mas gangliosidos que las de cabra y oveja. En cuanto al contenido de acido N-glicolilneuraminico, la leche de oveja y de cabra tienen porcentajes (con respecto al total de acidos sialicos) de 60-80% y 30-60% respectivamente, mientras que la de vaca lo tiene de 6-30%. Se ha analizado tambien la distribucion de los diferentes sialoglicoconjugados en la leche de vaca, destacando el elevado contenido de acidos sialicos unidos a oligosacaridos del calostro con respe...

The presence of climate denialism in the media has been studied especially in some countries such... more The presence of climate denialism in the media has been studied especially in some countries such as the United Kingdom or the United States, but it is gaining more and more interest in the academic field. The literature on the subject shows that this denialism is a minority phenomenon in the written press and on many occasions through subtle discourses. These characteristics pose a challenge for research. Considering the important role that truthful and scientifically contrasted information in the media could play in shaping social attitudes towards climate change, it is relevant to deepen the methodological tools that allow the study of this phenomenon. This study describes an exploratory approach to climate denialism in the written media, analyzing possible research strategies and methodologies. An aggregate search technique of key concepts in the specialized search engine Factiva between 2015 and 2020 was used to locate the denialist articles. Guided reading and discourse analys...

El factor tiempo: la urgencia Un asunto que los lideres politicos suelen soslayar en las cumbres ... more El factor tiempo: la urgencia Un asunto que los lideres politicos suelen soslayar en las cumbres de cambio climatico es que todos los Gases de Efecto Invernadero (GEI) que liberemos a la atmosfera tendran en algun momento un efecto sobre el aumento de temperatura/1. Este aumento, con un cierto margen de error, se puede cuantificar. Por eso lo realmente importante en las negociaciones climaticas, mas alla de grandes objetivos de reduccion a alcanzar en determinada fecha, son las emisiones acumuladas, es decir, la reduccion no para un determinado ano, sino en un periodo de anos establecido. Proponer una reduccion (respecto a 1990) de las emisiones de todo un periodo tomandolas en su conjunto conduce a esfuerzos mucho mas significativos, que comprometen desde el principio y de forma continuada, a la vez que evitan la tentacion de dejar para los ultimos anos la cabeza del leon de la reduccion de emisiones. Recientemente el G7 hacia un pomposo llamamiento a acabar el siglo XXI con cero e...