Multipotent bioflavonoid quercetin: Molecular targets and mechanism of action and nanotechnology applications in cancer, metabolic diseases and aging

Quercetin, a plant-based secondary metabolite widely present in fruits and vegetables, is a polyphenol belonging to the class of flavonoids. Studies for the past several decades have identified the great potential of this bioflavonoid in the prevention and treatment of a wide range of diseases. The biological effects of quercetin includes antimicrobial properties; antioxidative capacity; anti-allergic and anti-inflammatory activities; blood vessel protection; antitumor properties; antidiabetic and antiaging effects, anticataract and antineurodegenerative capacity; and protection against hypertension and cardiovascular diseases. Quercetin exerts this wide spectrum of effects by targeting several proteins/enzymes that are implicated in disease progression. Because of its outstanding safety profile and its availability in highly purified forms, the clinical implications for quercetin are growing rapidly. Even though quercetin is the major bioflavonoid in the human diet, its bioavailability has been debated. Recent studies to improve its bioavailability by combining it with vitamins or encapsulating it as nanoparticles are promising. This review mainly focuses on the molecular targets of quercetin and the mechanisms by which quercetin exerts its biological effects in the prevention and treatment of cancer, metabolic diseases and aging.