Quercetin: A Molecule of Great Biochemical and Clinical Value and Its Beneficial Effect on Diabetes and Cancer

Abstract

Quercetin belongs to the broader category of polyphenols. It is found, in particular, among the flavonols, and along with kaempferol, myricetin and isorhamnetin, it is recognized as a foreign substance after ingestion in contrast to vitamins. Quercetin occurs mainly linked to sugars with the most common compounds being quercetin-3-O-glucoside or as an aglycone, especially in the plant population. The aim of this review is to present a recent bibliography on the mechanisms of quercetin absorption and metabolism, bioavailability, and antioxidant and the clinical effects in diabetes and cancer. The literature reports a positive effect of quercetin on oxidative stress, cancer, and the regulation of blood sugar levels. Moreover, research-administered drug dosages of up to 2000 mg per day showed mild to no symptoms of overdose. It should be noted that quercetin is no longer considered a carcinogenic substance. The daily intake of quercetin in the diet ranges 10 mg–500 mg, depending on the type of products consumed. This review highlights that quercetin is a valuable dietary antioxidant, although a specific daily recommended intake for this substance has not yet been determined and further studies are required to decide a beneficial concentration threshold.

A Review on Polyphenols in Salicornia ramosissima with Special Emphasis on Their Beneficial Effects on Brain Ischemia

“…One of the most commonly studied flavonoids is quercetin, which is involved in several plant physiological processes, such as seed germination, photosynthesis and plant growth. Quercetin and its derivatives can present different biological activities due to modifications at significant positions of the quercetin molecule, such as glycosylation or methylation [ 70 ]. Quercetin was shown to protect human brain microvascular endothelial cells from I/R in vitro.…”

Anticancer Mechanism of Flavonoids on High-Grade Adult-Type Diffuse Gliomas

“…Other than being studied as a single treatment, few pre-clinical studies have reported that the combination of quercetin with conventional drugs such as TMZ enhanced the cytotoxic effect in high-grade adult-type diffuse glioma [ 26 , 67 , 68 ]. Numerous pre-clinical studies have also demonstrated that quercetin exhibits selective cytotoxicity in high-grade adult-type diffuse glioma cells against normal cells [ 179 , 180 ]. Several pre-clinical studies also reported that nanoparticles loaded with quercetin, when combined with TMZ, increase the cytotoxicity effects in both drug-sensitive and drug-resistant glioma cells [ 164 ].…”

Potential mechanisms of quercetin in cancer prevention: focus on cellular and molecular targets

“…Quercetin is a flavonoid and chemically it is a phenyl-substituted chromone composed of a basic skeleton of fifteen carbon atoms, composed of a chromium nucleus formed by the benzo ring A and the heterocyclic ring C, and in the aromatic ring B has a phenyl substitution [ 147 ]. Data have shown that the different substituents in rings A and B are responsible for the pharmacological activities of quercetin [ 148 ].…”

“…Although many researchers have attempted to highlight and understand the possible structure-anticancer activity correlation of quercetin, there is a scarcity of data to explain the relationship between chemical structure-cytotoxic and antitumor effect [ 149 ]. As a potential correlation, the hydroxylation pattern of the B ring in the chemical structure of quercetin would be responsible for its antiproliferative effects and inhibition of protein kinase B (AKT) [ 148 , 150 ] (Fig. 3 ).…”