Radioiodination, biological distribution, and docking study of diosmetin as a potential radiotracer for infection detection.

Staphylococcus aureus infections, particularly methicillin-resistant strains, pose major diagnostic challenges in differentiating septic from aseptic inflammation. This study aimed to radiolabel diosmetin (3',5,7-trihydroxy-4'-methoxyflavone), a natural flavonoid with antibacterial and anti-inflammatory properties, with iodine-131 (131I) and to evaluate its potential as a radiotracer for infection imaging. Diosmetin was isolated from Rosmarinus officinalis and radiolabeled with Na131I using the chloramine-T method. The radiochemical yield (RCY), and stability were assessed using TLC/HPLC. Molecular docking to COX-2 (PDB: 5KIR) was performed using the MOE software. In vitro binding to S. aureus was measured, and biodistribution studies were conducted in normal, inflamed, and infected Swiss Albino mice (n = 7 per subgroup) at 0.5-3 h post-injection. Target-to-non-target (T/NT) ratios were calculated from the %ID/g values. Radiolabeling achieved 95.8 ± 0.12% yield with >3 h of stability in PBS and serum. Docking revealed a strong COX-2 affinity. In vitro binding to S. aureus reached 52 ± 1.5%. In infected mice, [131I]DSM accumulated selectively in the infected muscle (3.85 ± 0.10%ID/g at 2 h), yielding a T/NT ratio of 7.7, which was double that in inflamed tissue (3.7). Rapid blood clearance, predominant renal excretion, and low thyroid uptake confirmed the in vivo stability. [131I]Diosmetin was prepared with high yield and stability, demonstrated selective uptake at infectious foci, and enabled clear differentiation between septic and aseptic inflammation. These findings support its potential as a promising radiotracer for infection imaging applications.