Quercetin is an important phytochemical which received a lot of attention. Quercetin occurs in many common foods such as onions, apples and tea. Especially onions are rich in quercetin. Epidemiological studies suggest that consumption of fruit and vegetables results in a reduced breast cancer risk. Quercetin has strong antioxidant properties and may prevent the initiation of carcinogenesis. Quercetin has other potential health benefits such as stopping of cell cycle, apoptosis of transformed cells and reducing microtubule polymerization. This study was to first to prove that quercetin inhibits angiogenesis by a combined action of suppression of endothelial nitric oxide synthase and early M-phase cell cycle arrest. Endothelial nitric oxide synthase produces nitric oxide, which acts as a signalling molecule and stimulates the formation of new blood vessels, required for tumor to grow. Nitric oxide is also an inducer of vasodilatation.
Limiting endothelial cell growth is also a mechanism to reduce tumour growth. During the M-phase of the cell cycle mitotic microtubules are formed which are needed to segregate the chromosomes. Some phytochemicals, such as quercetin, might act as antimitotic compounds by disrupting microtubules formation.
This study involved both in vivo and in vitro tests. For the in vitro test, bovine aortic endothelial cells were exposed to quercetin and were tested for endothelial nitric oxide synthase and phosphorylation status. Quercetin inhibited the endothelial dell proliferation in a dose dependent manner. They found that quercetin suppressed endothelial nitric oxide synthase activity and phosphorylation. Chronic exposure of quercetin resulted in early-M-phase arrest by disruption of cellular microtubule polymerization.
For the in vitro test, quercetin was fed to female mice with mammary tumours and Matrigel implants. Quercetin reduced breast tumor associated angiogenesis and reduced blood vessel growth. The treatment of the mice with quercetin did not result in other signs of toxicity.
The obtained results showed that quercetin inhibits angiogenesis by a combined action of suppression of endothelial nitric oxide synthase and early M-phase cell cycle arrest. Quercetin could play an important role as a chemopreventive agent for carcinogenesis.
Source: Jackson SJ and Venema RC. Quercetin inhibits eNOS, microtubule polymerization, and mitotic progression in bovine aortic endothelial cells.. Journal of Nutrition, 2006 May;136(5):1178-84
