New research explains the antihypertensive properties of green and black tea

A new study from the University of California, Irvine (USA) explains the antihypertensive properties of compounds in green and black tea, that is, how they relax blood vessels by activating ion channel proteins in the wall of these vessels. . The discovery could lead to the design of new drugs to lower blood pressure.

Because up to one-third of the world's adult population has hypertension, and this condition is considered the number one modifiable risk factor for global cardiovascular disease and premature mortality, new approaches to treating hypertension have enormous potential to improve global public health. Previous studies have shown that drinking green or black tea can lower blood pressure by a small but consistent amount, and catechins were previously found to contribute to this property.

The research results revealed that two catechin-type flavonoid compounds (epicatechin gallate and epigallocatechin-3 gallate) found in tea each activate a specific type of ion channel protein called KCNQ5, which allows ions to of potassium diffuse out of the cells to reduce cellular excitability.

Because KCNQ5 is found in the smooth muscle that lines blood vessels, its activation by tea catechins was also predicted to relax blood vessels, a prediction confirmed by collaborators at the University of Copenhagen.

Published in Cellular Physiology and Biochemistry, the discovery was made by the laboratory of Geoffrey Abbott, PhD, professor in the Department of Physiology and Biophysics at the UCI School of Medicine. Kaitlyn Redford, graduate student in the Abbott laboratory.

"We discovered through the use of computer modeling and mutagenesis studies that specific catechins bind to the foot of the voltage sensor, which is the part of KCNQ5 that allows the channel to open in response to cellular excitation. This binding allows the channel to open much more easily and earlier in the cell excitation process," said the researcher.

Identification of KCNQ5 as a novel target for the hypertensive properties of tea catechins may facilitate optimization of medicinal chemistry to improve potency or efficacy. In addition to its role in controlling vascular tone, KCNQ5 is expressed in various parts of the brain, where it regulates electrical activity and signaling between neurons.

There are variants of the pathogenic KCNQ5 gene that impair the function of its channel and, in doing so, cause epileptic encephalopathy, a developmental disorder that is severely debilitating and causes frequent seizures. Because catechins can cross the blood-brain barrier, the discovery of their ability to activate KCNQ5 may suggest a future mechanism to repair disrupted KCNQ5 channels to ameliorate brain excitability disorders arising from their dysfunction.

Tea has been produced and consumed for over 4.000 years and currently over 2.000 billion cups of tea are drunk each day around the world, second only to water in terms of volume consumed by people around the world. The three commonly consumed caffeinated teas (green, oolong and black) are produced from the leaves of the evergreen species 'Camellia sinensis', the differences arising from the different degrees of fermentation during tea production.

Black tea is commonly mixed with milk before being consumed in countries such as the United Kingdom and the United States. The researchers in the present study found that when black tea was applied directly to cells containing the KCNQ5 channel, the addition of milk prevented the beneficial KCNQ5-activating effects of the tea.

However, "we do not believe that this means that one should avoid milk when drinking tea to take advantage of the beneficial properties of tea. We are confident that the environment in the human stomach will separate the catechins from the proteins and other molecules in the milk that otherwise they would block the beneficial effects of catechins.

This hypothesis is confirmed by other studies that show the antihypertensive benefits of tea independently of milk consumption. The team also found, using mass spectrometry, that heating green tea to 35 degrees Celsius alters its chemical composition in a way that makes it more effective at activating KCNQ5.

"Regardless of whether the tea is consumed iced or hot, this temperature is reached after drinking the tea, since the human body temperature is about 37 degrees Celsius. Therefore, by simply drinking tea we activate its beneficial antihypertensive properties," concludes Abbott.