Black tea is one of the highest sources of flavonoid quercetin, which can protect blood vessels against oxidant induced damage, Australian researchers found.
“This study was a preliminary study in cells and isolated mouse vessels, so more work is still needed to ascertain the beneficial effects of quercetin against CVD,” said Dr Natalie Ward and Professor Kevin Croft from the University of Western Australia.
“However our findings have suggested that quercetin is able to protect vessels against oxidant induced damage,” they said.
According to the study, flavonoids are metabolised rapidly by methylation or glucuronidation after ingestion, which can alter their biological activity, a media report said.
The effects of quercetin on endothelial cell functions are in part mediated via adenosine monophosphate-activated protein kinase (AMPK), a key enzyme in cellular energy homeostasis that affects fatty acid oxidation.
“AMPK is a cellular energy sensor that responds to stress situations and potentially protect the cell from damage,” they said.
“It is present in a number of cell types and is thought to be involved in numerous signalling pathways,” the researchers said.
“At this stage the exact mechanism for how quercetin and other flavonoids affect AMPK is unclear, although it is thought to be in part, through increased phosphorylation at important activation sites,” they said.
The study found that quercetin and its metabolites can induce activation of AMPK and eNOS in human aortic endothelial cells, and lead to an increase in the concentrations of S-nitrosothiols and nitrite in cell culture media.
“S-nitrosothiols and nitrite are indices of nitric oxide production by the cell. Nitric oxide is an important vasodilator that is required for the normal function of blood vessels,” the researchers explained.
They said quercetin also works to protect vessels against hypochlorous acid-induced endothelial dysfunction in isolated arteries.
“We believe [quercetin] works by upregulating Heme-oxygenase which is an antioxidant enzyme that can then protect the vessels against oxidant induced damage,” they said.
The study was published in the journal of Biochemical Pharmacology.