[en] INTRODUCTION: acute cellular rejection (ACR) is an important complication after heart transplantation (HTx). Endomyocardial biopsy is the reference method for the early detection of this ACR, but it has important limitations. These include being invasive, the probable sampling error, the high cost and the subjective interpretation of the pathologist, which cause great variability in the final results. Therefore, it would be very useful to find a non-invasive biomarker for detecting ACR in the transplant patient. Among the possible candidates are circulating microRNAs. The main objective of the central study of this thesis is to discover and validate microRNAs in serum samples for the early detection of ACR in the follow-up of HTx. METHODS: 121 HTx patients were included in this prospective, observational, single-center study. RCA based on EMB was classified according to the International Society of Heart and Lung Transplantation (ISHLT) in 2004, with 4 grades: "0R" without rejection, "1R" mild rejection, "2R" moderate rejection, "3R" rejection serious. Initially, in an initial search phase, an experiment was carried out with microRNA expression profiles in the serum of pre-RCA patients "0RS1", during rejection "2RS2" and after rejection "0RS3". The entire episode was called "0RS1 →2RS2 →0RS3". A total of 179 microRNAs in each serum were analyzed by RT-qPCR (Reverse Transcriptase quantitative Polymerase Chain Reaction) and those microRNAs with a significant rise/fall pattern (or vice versa) during the episode "0RS1 →2RS2 →0RS3" were selected. The next validation phase will check the diagnostic efficacy to detect RCA of the selected microRNAs. For this, new serum samples will be sought to form two new groups of patients, a group without "NoR" rejection and another with ACR (BEM≥2R). RESULTS: in the initial search phase, microRNAs were analyzed in a total of 21 episodes of RCA "0RS1 →2RS2 →0RS3", and their respective serum samples (n = 63). Among the 179 microRNAs analyzed, only miR-181a-5p met the criteria for significant up- and down-regulation and therefore, the only microRNA selected for the next phase. In validation, miR-181a-5p was analyzed in 45 samples with RCA and 45 samples without RCA, being found significantly overexpressed in the group with RCA. The miR-181a-5p candidate also achieved an area under the curve AUC = 0.804 (95% CI: 0.707-0.880), and a sensitivity and specificity of 78% and 76%, respectively, with a high negative predictive value (98%). CONCLUSION: miR-181a-5p has demonstrated very good qualities as a non-invasive biomarker of ACR in HTx. A high negative predictive value together with a reduced cost and simplicity of analysis would justify its use as an aid in the management and monitoring of the heart transplant patient.

[gl] INTRODUCIÓN: o rexeitamento celular agudo (RCA) é unha complicación importante despois do trasplante cardíaco (TxC). A biopsia endomiocárdica (BEM) é o método de referencia para a detección precoz deste RCA, pero ten importantes limitacións. Estes inclúen ser invasivo, o probable erro de mostraxe, o alto custo e a interpretación subxectiva do patólogo, que provocan unha gran variabilidade nos resultados finais. Polo tanto, sería moi útil atopar un biomarcador non invasivo para detectar RCA no paciente trasplantado. Entre os posibles candidatos están os microRNA circulantes. O obxectivo principal do estudo central desta tese é descubrir e validar microRNA en mostras de soro para a detección precoz de RCA no seguimento de TxC. MÉTODOS: 121 pacientes con HTx foron incluídos neste estudo prospectivo, observacional, dun centro. A RCA baseada en BEM foi clasificada segundo a Sociedade Internacional de Trasplante de Corazón e Pulmón (ISHLT) en 2004, con 4 graos: "0R" sen rexeitamento, "1R" rexeitamento leve, "2R" rexeitamento moderado, "3R" rexeitamento grave. Inicialmente, nunha fase de busca inicial, realizouse un experimento con perfís de expresión de microRNA nos soros de pacientes pre-RCA "0RS1", durante RCA "2RS2" e post-RCA "0RS3". Todo o episodio chamouse "0RS1 →2RS2 →0RS3". Analizáronse 179 microRNA en cada soro mediante RT-qPCR (Reacción en cadea da polimerase cuantitativa da transcriptase inversa) e seleccionáronse aqueles microARN cun patrón de subida/descenso significativo (ou viceversa) durante o episodio "0RS1 →2RS2 →0RS3". A seguinte fase de validación comprobará a eficacia diagnóstica para detectar RCA dos microRNA seleccionados. Para iso, buscaranse novas mostras de soro para formar dous novos grupos de pacientes, un grupo sen rexeitamento "NoR" e outro con RCA (BEM≥2R). RESULTADOS: na fase de busca inicial analizáronse os microRNA nun total de 21 episodios de RCA "0RS1 →2RS2 →0RS3", e as súas respectivas mostras de soro (n = 63). Entre os 179 microANAs analizados, só o miR-181a-5p cumpriu os criterios para unha regulación significativa ao alza e á baixa e, polo tanto, o único microRNA seleccionado para a seguinte fase. Na validación, miR-181a-5p analizouse en 45 mostras con RCA e as mesmas sen RCA, encontrándose significativamente sobreexpresada no grupo con RCA. O candidato miR-181a-5p tamén logrou unha área baixo a curva de 0,804 (IC 95%: 0,707-0,880), e unha sensibilidade e especificidade do 78% e 76%, respectivamente, cun alto valor preditivo negativo (98%). CONCLUSIÓN: miR-181a-5p demostrou moi boas calidades como biomarcador non invasivo de RCA en TxC. Un alto valor preditivo negativo xunto cun custo reducido e sinxeleza de análise xustificarían o seu uso como axuda na xestión e seguimento do paciente trasplantado cardiaco.