Circadian Rhythm of the Human Plasma Proteome

Background Plasma is the most used clinical specimen, yet circadian variation in plasma proteins remains largely unexplored. We aimed to identify circadian-regulated proteins in healthy individuals and assess their potential diagnostic implications, and highlight how circadian awareness can advance future biomarker research. Methods Twenty-four healthy young individuals were studied under highly controlled conditions. Venous blood was drawn every three hours over a 24-hour period, yielding 216 samples, of which 208 high-quality plasma samples were analyzed via high-throughput mass spectrometry. The missing data were filtered and imputed, and rhythmicity was assessed using Cosinor-based modeling with Benjamini-Hochberg correction. Tissue and pathway enrichment analyses were performed using the DAVID functional annotation tool. Findings Of 523 proteins that passed quality thresholds, 138 (~ 26%) exhibited significant circadian oscillations. Tissue enrichment analysis revealed that most rhythmic proteins originated from the liver and platelets, with additional enrichment in a variety of tissue types. Pathway enrichment showed circadian regulation of hemostasis, immune signaling, integrin-mediated processes, glucose metabolism, and protein synthesis. Notably, 36 clinically utilized biomarkers, including albumin, amylase, and cystatin C exhibited circadian variation, suggesting that failing to account for temporal fluctuations may reduce diagnostic precision. Interpretation These findings demonstrate that over one-quarter of the human plasma proteome is under circadian control. Such oscillations might have direct clinical implications, as the time-of-day may alter biomarker accuracy. Incorporating circadian timing into diagnostic and research protocols, through standardized sampling or time-sensitive reference intervals, could improve patient care and inform future biomarker discoveries. Further research in larger, more diverse populations is needed to generalize these results and streamline circadian-aware practices in clinical practice.