Biomarcadores de imagen, imagen cuantitativa y bioingeniería / Imaging biomarkers, quantitative imaging, and bioengineering

Los biomarcadores de imagen definen características objetivas extraídas de las imágenes médicas, relacionadas con procesos biológicos normales, enfermedades o respuestas terapéuticas. Para desarrollar un biomarcador de imagen es necesario realizar una serie de pasos destinados a validar su relación con la realidad estudiada y controlar su validez, tanto clínica como técnica. Este proceso incluye la definición de pruebas de concepto y de mecanismo; la adquisición estandarizada y optimizada de imágenes anatómicas, funcionales y moleculares; el análisis de los datos mediante modelos computacionales; la visualización adecuada de los resultados; la obtención de medidas estadísticas apropiadas; y la realización de pruebas de principio, eficacia y efectividad. Nuestro objetivo en este trabajo es mostrar los pasos que deben establecerse para aplicar adecuadamente los biomarcadores de imagen, desde su concepción teórica hasta su implantación asistencial, en un entorno hospitalario. Para ello se planteará como ejemplo la valoración de la angiogénesis del cartílago articular (AU)

Imaging biomarkers define objective characteristics extracted from medical images that are related to normal biological processes, diseases, or the response to treatment. To develop an imaging biomarker, it is necessary to carry out a series of steps to validate its relation with the reality studied and to check its clinical and technical validity. This process includes defining tests for the concepts and mechanisms; obtaining standardized and optimized anatomic, functional, and molecular images; analyzing the data with computer models; displaying data appropriately; obtaining the appropriate statistic measures; and conducting tests on the principle, efficacy, and effectiveness. In this article, we aim to explain the steps that must be established to enable biomarkers to be correctly applied, from their theoretical conception to their clinical implementation. To this end, we use the evaluation of angiogenesis in articular cartilage as an example (AU)

[Imaging biomarkers, quantitative imaging, and bioengineering]. / Biomarcadores de imagen, imagen cuantitativa y bioingeniería.

Imaging biomarkers define objective characteristics extracted from medical images that are related to normal biological processes, diseases, or the response to treatment. To develop an imaging biomarker, it is necessary to carry out a series of steps to validate its relation with the reality studied and to check its clinical and technical validity. This process includes defining tests for the concepts and mechanisms; obtaining standardized and optimized anatomic, functional, and molecular images; analyzing the data with computer models; displaying data appropriately; obtaining the appropriate statistic measures; and conducting tests on the principle, efficacy, and effectiveness. In this article, we aim to explain the steps that must be established to enable biomarkers to be correctly applied, from their theoretical conception to their clinical implementation. To this end, we use the evaluation of angiogenesis in articular cartilage as an example.

Inhibition of translation and cell growth by minigene expression.

A random five-codon gene library was used to isolate minigenes whose expression causes cell growth arrest. Eight different deleterious minigenes were isolated, five of which had in-frame stop codons; the predicted expressed peptides ranged in size from two to five amino acids. Mutational analysis demonstrated that translation of the inhibitory minigenes is essential for growth arrest. Pulse-labeling experiments showed that expression of at least some of the selected minigenes results in inhibition of cellular protein synthesis. Expression of the deleterious minigenes in cells deficient in peptidyl-tRNA hydrolase causes accumulation of families of peptidyl-tRNAs corresponding to the last minigene codon; the inhibitory action of minigene expression could be suppressed by overexpression of the tRNA corresponding to the last sense codon in the minigene. Experimental data are compatible with the model that the deleterious effect of minigene expression is mediated by depletion of corresponding pools of free tRNAs.

lambda bar minigene-mediated inhibition of protein synthesis involves accumulation of peptidyl-tRNA and starvation for tRNA.

Expression of the bacteriophage lambda two-codon, AUG AUA, barI minigene (bar+) leads to the arrest of protein synthesis in cells defective in peptidyl-tRNA hydrolase (Pth). It has been hypothesized that translation of the bar+ transcript provokes premature release and accumulation of peptidyl-tRNA (p-tRNA). Inhibition of protein synthesis would then result from either starvation of sequestered tRNA or from toxicity of accumulated p-tRNA. To test this hypothesis and to investigate the cause of arrest, we used a coupled in vitro transcription-translation system primed with DNA containing bar+ and the beta-lactamase-encoding gene of the vector as a reporter. The results show that expression of bar+ minigene severely inhibits beta-lactamase polypeptide synthesis by Pth-defective extracts and partially inhibits synthesis by wild-type extracts. Fractions enriched for Pth, or a homogeneous preparation of Pth, prevented and reversed bar+-mediated inhibition. A mutant minigene, barA702, which changes the second codon AUA (Ile) to AAA (Lys), was also toxic for Pth-defective cells. Expression of barA702 inhibited in vitro polypeptide synthesis by Pth-defective extracts and, as with bar+, exogenous Pth prevented inhibition. Addition of pure tRNALys prevented inhibition by barA702 but not by bar+. Expression of bar+ and barA702 led to release and accumulation of p-tRNAIle and p-tRNALys respectively but bar+ also induced accumulation of p-tRNALys. Finally, bar+ stimulated association of methionine with ribosomes probably as fMet-tRNAfMet and the accumulation of methionine and isoleucine in solution as peptidyl-tRNA (p-tRNA). These results indicate that minigene-mediated inhibition of protein synthesis involves premature release of p-tRNA, misincorporation of amino acyl-tRNA, accumulation of p-tRNAs and possibly sequestration of tRNAs.