jueves, 22 de marzo de 2012

cantidades adecuadas de nutrientes: transcriptómica

Tenemos una revisión estupenda de la búsqueda de la "verdad": qué alimentos son buenos, cuáles no tanto, cuánta cantidad hay que comer de cada uno, cuánta cantidad no debemos superar... Medido de la manera más objetiva posible: Análisis transcriptómicos, valorando los cambios en el ADN y la expresión genética. A continuación expongo algunos de los resultados interesantes en castellano.


Transcriptome analysis in benefit–risk assessment of micronutrients and bioactive food components

Jaap Keijer1, Yvonne G. J. van Helden1,2,3, Annelies Bunschoten1

and Evert M. van Schothorst1

DOI 10.1002/mnfr.200900304 Mol. Nutr. Food Res. 2010, 54, 240–248

The establishment of functional effects due to variation in concentrations of micronutrients in our diet is difficult since they are often not immediately recognized as being healthy or unhealthy. Indeed, effects induced by micronutrients are hard to identify and therefore the establishment of the recommended daily intake, the optimal intake and the upper limit pose a challenge. For bioactive food components this is even more complicated. Whole-genome transcriptome analysis is highly suitable to obtain unbiased information on potential affected biological processes on a whole-genome level. Here, we will describe and discuss several aspects of transcriptome analysis in benefit–risk assessment, including effect size, sensitivity and statistical power, that have to be taken into account to faithfully identify functional effects of micronutrients and bioactive food components."

Se sabe hace tiempo que los micronutrientes afectan nuestra salud. Cómo la afectan en un rango de concentración está menos claro. La deficiencia y el exceso producen cambios fisiológicos y efectos patológicos. Entre estos extremos pueden ocurrir muchos cambios en la salud según la concentración. Al menos se intentan establecer los límites para que el consumo no sea perjudicial.

·       RDI: recomendación diaria es la cantidad mínima para que el 97% de la población no tenga carencias.

·      UL: es la dosis máxima a partir de la cual se han observado problemas de salud o efectos secundarios "peligrosos".

·       La ingesta óptima beneficiosa es muy difícil de establecer, sobre todo teniendo en cuenta que son parámetros que deben ser individualizados.

·      Además aún hay muchos fitoquímicos (componentes de los alimentos) que se desconocen por lo que es necesario mejorar la ciencias ómicas para poder establecer los parámetros óptimos de ingesta.

El único ejemplo realmente determinado y avalado hasta ahora de que un micronutrietne que supera la RDI tiene efectos beneficiosos para la salud es el SELENIO.

La carencia de selenio provoca la enfermedad de Kashin e hipotiroidismo, por ejemplo, y el exceso causa una toxicidad conocida como Seleniosis. La toma de cantidades mayores de selenio han demostrado beneficios en los estudios pero el mecanismo no es claro. Se ha visto cambios en la expresión genética que han aumentado el sistema inmune y han mejorado el colon...

Se ha realizado ANÁLISIS DEL TRANSCRIPTOMA, confirmación de datos por qRT-PCR y análsis estadístico. Por ejemplo una dieta baja en grasas hace que se expresen más de 15000 genes, comparando una dieta alta en grasa y todos estos genes deben analizarse buscando su función.

5603 genes se expresan con la suplementación de polifenoles.

1650 genes cambian con el té verde.

1683 con cantidad equimolar de resveratrol

977 con quercetina

Esto nos indica que la suplementación de estos fitoquímicos produce un efecto muy pequeño en comparación con, por ejemplo una dieta alta o baja en grasa!!!

Esto teniendo en cuenta que a pesar de todo la transcriptómica también tiene errores. Es una prueba fiable al ser "in vivo" pero hay que tener en cuenta las diferencias entre individuos, razas, y los cambios en expresión genética de diferentes células: sangre, músculo... habría que analizar una población muy grande y todos sus tipos de células.

Concluding remarks

In conclusion, micronutrients and bioactive food components may have functional effects that only become apparent in later life, that is, after chronic differences in intake, or under conditions of stress, affecting fitness and wellbeing. While for intake between RDI and UL no overt differences in health can be expected, these differences may be very important for healthy aging and resistance to disease. They may have particular beneficial effects on the overarching processes; metabolic stress, oxidative stress, inflammatory stress and psychological stress [34]. To be able to establish functional health effects of micronutrients and bioactive food components, an overview of mechanistic effects is needed and transcriptome analysis is highly suited as a first step. When applied correctly, it has the power to detect the relatively small differences in gene expression that are induced by micronutrients and food bioactive compounds. It is however not a miracle technique. It takes experience andhard work to use it properly and to generate true and usefuldata. But when used sensibly, it is highly powerful and will generate data that will contribute to the establishment of

functional effects and mechanisms of action of micronutrients and bioactive food components, a prerequisite for their application in health promoting functional foods.


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