Therapeutic applications of quercetin-metallic complexes: a review

Flavonoids, especially quercetin, are widely recognized for their antioxidant, anti-inflammatory, anti-microbial, anti-diabetic, and anti-tumor properties, but their clinical application is limited by poor permeability. Different techniques of permeability enhancement of quercetin, i.e., preparation of phytosomes, conjugation with glucose, and interaction of piperine, are reported extensively, but formation of metal complexes is considered more precise and reliable. This review focuses on research conducted on the chelation of quercetin with metals, i.e., copper (II), zinc (II), iron and ruthenium. In-vitro and in-vivo therapeutic activities, biomedical applications of metal/quercetin inclusion complexes and discussions of stability concerns of quercetin alone and its metallic complexes. Conjugation of metals with quercetin augments its potential to the next level. Numerous studies revealed that quercetin/copper (Q/Cu) and quercetin/zinc (Q/Zn) can become efficacious candidates in acute myeloid leukaemia, orthopaedics and severe acute respiratory syndrome coronavirus (SARS-CoV) infection.