Systemic Molecular Alterations of TP53, SIRT-1, and miR-34a Expression in Atrial Fibrillation: A Prospective Exploratory Biomarker Study

p53, miR-34a, and SIRT-1 are involved in cellular stress responses, senescence, and inflammation—processes central to the pathophysiology of atrial fibrillation (AF). In this study, circulating TP53 and SIRT-1 serum miR-34a expression were determined in patients with and without AF, in order to assess their associations with AF. We also checked their potential diagnostic utility as systemic biomarkers associated with AF. The study included 189 adults, 94 AF+, 95 AF−. Clinical, anthropometric, and biochemical data were collected. Whole-blood TP53 and SIRT-1 mRNA expression and serum miR-34a expression were quantified by RT-qPCR. ROC analysis and Youden-derived odds ratios assessed exploratory diagnostic performance. AF patients had significantly higher expression of TP53 (0.0352 vs. 0.0253; p < 0.001) and miR-34a (0.0215 vs. 0.0099; p < 0.001), but significantly lower expression of SIRT-1 (0.0079 vs. 0.0145; p < 0.001). The level of SIRT-1 expression showed the highest discriminatory performance (exploratory AUC = 0.6987; p < 0.0001). TP53 expression levels exceeding 0.0295 were associated with nearly threefold higher odds of AF (OR = 2.92, 95% CI: 1.61–5.28, p = 0.0006), whereas the expression levels of SIRT-1 and miR-34a were not significantly associated with AF in cut-off analysis. In the AF group, a positive correlation was found between the expression of TP53 and SIRT-1 (Rho = 0.3609, p < 0.001); however, it was not consistent with a canonical model of miR-34a-mediated SIRT-1 suppression. In turn, the expression of miR-34a correlated positively with age and C-reactive protein level and negatively with estimated glomerular filtration rate (eGFR). The obtained results suggest that AF is associated with altered expression of circulating TP53, SIRT-1, and miR-34a. However, due to the fact that the expression levels were measured in peripheral compartments, and not in atrial tissue, the obtained results should not be interpreted as direct evidence of AF-related atrial remodeling. For these reasons, further investigations involving simultaneous measurements of the TP53/miR-34a/SIRT-1 regulatory axis, both in the circulating compartment and atrial tissue, should be performed.