Black tea is more effective than green tea in prevention of radiation-induced oxidative stress in the aorta of rats

Abstract

In the work, the effect of black tea on oxidative stress induced in the aorta by irradiation was studied. The efficiency of black and green tea types was compared, and the effect of the main green tea components (-)-epigallocatechin galate (EGCG) and (-)-epigallocatechin (EGC) on the aorta was studied. The activity of ACE in rat aorta segments was determined by measuring the hydrolysis of hippuryl-L-histidyl-L-leucine, and the production of ROS was estimated from the oxidation of dichlorodihydrofluorescein. Black tea prevented the radiation-induced activation of the ACE and suppressed increased ROS production in the aorta of irradiated rats. The IC₅₀ value for the suppression of the irradiation-induced increase in ACE activity is 1 ml of black tea brewed at a rate of 0.17 g/100 ml. Black tea is 12 times more effective than green tea. The administration of both catechin derivatives from green tea to rats leads to an increase in the activity of ACE and the formation of ROS in the aorta. The dose that provided half maximum activation of ACE (EC₅₀) on intraperitoneal (i. p.) injection of galloylated catechins was found to be the same, 0.06-0.07 μg/kg of body weight. Upon intragastric gavage of EGCG, the EC₅₀ value was by one order of magnitude higher, 0.8 μg/kg. Black tea was more effective than green tea in prevention a radiation-induced increase of ACE activity and oxidative stress in the aorta. This difference was explained by a low content of galloylated catechins in black tea.

Keywords: Angiotensin-converting enzyme; Aorta; Black tea; Ionizing radiation; Reactive oxygen species.