Hypothesis / aims of study
Detrusor underactivity (DU) is characterized by impaired bladder contractility resulting in prolonged voiding and incomplete bladder emptying. DU is frequently observed in elderly men and contributes to lower urinary tract symptoms (LUTS). However, its diagnosis currently requires invasive urodynamic study (UDS), limiting clinical use. Differentiating DU from bladder outlet obstruction (BOO) is often difficult because both conditions present with similar voiding symptoms. DU without obstruction, referred to as pure DU, may represent a distinct pathophysiological condition involving age-related changes, ischemia, and impaired neural regulation. Despite its clinical importance, the molecular mechanisms underlying pure DU remain poorly understood, and reliable non-invasive diagnostic biomarkers have not been established. MicroRNAs (miRNAs) regulate gene expression and have emerged as promising biomarkers due to disease-specific expression patterns and stability in body fluids. Urinary extracellular vesicles (uEVs) contain miRNAs derived from the urinary tract and may reflect molecular changes in the bladder. This study aimed to identify urinary miRNAs associated with pure DU and evaluate their potential as non-invasive biomarkers distinguishing pure DU from BOO-related conditions.
Study design, materials and methods
This exploratory cross-sectional study consisted of a discovery phase and a validation phase. In the discovery phase, urinary extracellular vesicle-derived miRNA profiles were analyzed using microarray technology. Participants were classified into four groups: pure DU (n=4), BOO (n=4), young healthy controls (n=4), and older healthy controls (n=4). Differentially expressed miRNAs specific to pure DU were identified using fold change criteria and statistical analysis. In the validation phase, candidate miRNAs identified in the discovery cohort were evaluated in an independent cohort consisting of pure DU (n=16) and non-pure DU (n=15), including BOO alone or DU with BOO. Quantitative RT-PCR (RT-qPCR) was used to validate candidate miRNAs. Receiver operating characteristic (ROC) curve analysis evaluated diagnostic performance, and optimal cutoff values were determined using the Youden index. Clinical and urodynamic parameters were compared between groups stratified by cutoff values.
Results
Microarray analysis identified 28 miRNAs with differential expression specific to pure DU compared with BOO and healthy controls (Figure 1). Among these, four candidate miRNAs (miR-1273g-3p, miR-3940-5p, miR-4668-5p, and miR-3613-3p) were selected for validation. In the validation cohort, RT-qPCR analysis showed that miR-1273g-3p and miR-3940-5p were significantly downregulated in patients with pure DU compared with the non-pure DU group (p=0.003 and p=0.045). The other candidate miRNAs did not show consistent results and were excluded. ROC curve analysis showed that miR-1273g-3p had good diagnostic performance with an area under the curve (AUC) of 0.804 (95% CI 0.640–0.968). Using a cutoff value of 14.7, sensitivity was 100% and specificity was 60%. miR-3940-5p showed moderate diagnostic accuracy with an AUC of 0.713 (95% CI 0.526–0.899). Using the cutoff value for miR-1273g-3p, patients in the low-expression group showed significantly lower bladder outlet obstruction index and bladder contractility index (p=0.033 and p=0.021). No significant differences were observed in age, body mass index, maximum flow rate, or post-void residual urine volume (Table1).
Interpretation of results
Urinary miRNA expression profiles differ between pure DU and BOO-related conditions, suggesting distinct molecular mechanisms. The downregulation of miR-1273g-3p and miR-3940-5p in pure DU may reflect impaired pathways associated with detrusor contractility. In particular, miR-1273g-3p showed good diagnostic accuracy and correlations with urodynamic parameters reflecting bladder contractile function. These findings suggest that urinary miRNAs derived from extracellular vesicles may serve as molecular indicators of detrusor dysfunction.