Re-evaluating variability of circulating miR-122 in healthy volunteers: Implications for biomarker qualification in drug-induced liver injury

Drug-induced liver injury (DILI) remains a major challenge in clinical practice and drug development, and reliable biomarkers are still needed. MicroRNA-122 (miR-122) has shown promise, but reported inter-individual variability in healthy populations has raised concerns about its clinical utility. We analysed circulating miR-122 levels in healthy volunteers across three European sites (Antwerp, n = 96; Brussels, n = 124; and Leeds, n = 60) using small RNA sequencing within the TransBioLine programme. Only modest regional differences were observed (miR-122-5p ICC 0.864; miR-122-3p ICC 0.849). Importantly, intra-individual miR-122 levels were stable over time (CV 10.7% and 16.5%, respectively), even under physiological perturbations such as fasting and postprandial states. Our findings suggest that previously reported miR-122 variability may largely reflect analytical factors, including normalization strategies, rather than biological instability. miR-122 is a robust biomarker for liver injury when appropriate analytical approaches and individual baseline levels are considered, supporting its application in clinical pharmacology and drug development.