Serum miR-208 as a biomarker of drug-induced myocardial injury in rats: A histopathology-referenced threshold analysis

Early identification of drug-induced cardiotoxicity (DICT) is crucial for efficient safety assessment in pharmaceutical development. While histopathology serves as the standard for evaluating structural injury, biomarkers capable of detecting toxicity at an early stage are highly desirable. This study evaluated the utility of circulating miR-208 as a highly specific biomarker for cardiotoxicity screening and aimed to establish a quantitative preclinical diagnostic criterion. First, analysis of a rat miRNA expression atlas confirmed that miR-208 is exclusively enriched in the heart, lacking the skeletal muscle background expression that frequently confounds conventional markers. Subsequently, Sprague-Dawley rats were administered five diverse cardiotoxic drugs (isoproterenol, carbofuran, allylamine, doxorubicin, and Compound A) to profile serum miR-208 responses against histopathological findings. Receiver Operating Characteristic (ROC) analysis across these models demonstrated high diagnostic accuracy (AUC = 0.91), establishing a robust cutoff value that provides 95% specificity for preclinical evaluation. Notably, in doxorubicin-treated rats, an upward trend in serum miR-208 levels was observed as early as 24 h post-administration. This early molecular response preceded the onset of structural cell death detectable by histopathology and any macroscopic functional decline measurable by echocardiography. These findings demonstrate that miR-208 is a highly specific and accurate screening tool capable of capturing early cardiotoxic signals, thereby providing an objective and powerful diagnostic advantage in preclinical safety assessments.