Green tea is one of the most widely consumed beverages worldwide. Green tea catechins are associated with a delay in aging. In experiments performed in Caenorhabditis elegans nematodes, scientists from ETH Zurich and elsewhere investigated the impact of the most abundant green tea catechins, epigallocatechin gallate (EGCG) and epicatechin gallate (ECG), on health and aging.
A concentration of 2.5 μM EGCG and ECG enhanced health- and lifespan as well as stress resistance in Caenorhabditis elegans. Catechins hampered mitochondrial respiration in Caenorhabditis elegans after 6-12 hrs and the activity of complex I in isolated rodent mitochondria. The impaired mitochondrial respiration was accompanied by a transient drop in ATP production and a temporary increase in ROS levels in Caenorhabditis elegans. After 24 hrs, mitochondrial respiration and ATP levels got restored, and ROS levels even dropped below control conditions. The lifespan increases induced by EGCG and ECG were dependent on AAK-2/AMPK and SIR-2.1/SIRT1, as well as on PMK-1/p38 MAPK, SKN-1/NRF2, and DAF-16/FOXO. Long-term effects included significantly diminished fat content and enhanced SOD and CAT activities, required for the positive impact of catechins on lifespan. Image credit: Tian et al., doi: 10.18632/aging.203597.
“ECG and EGCG are considered antioxidants, which means they counteract or prevent oxidative stress in the body caused by aggressive free radicals of oxygen,” said senior co-author Professor Michael Ristow, a researcher in the Department of Health Sciences and Technology at ETH Zurich and the Department of Human Nutrition at the Friedrich Schiller University Jena, and his colleagues.
“Until now, it was assumed that these catechins neutralize free radicals and thus prevent damage to cells or DNA.”
“One source of oxygen free radicals is metabolism; for example, when the mitochondria — the powerhouses of the cell — are working to produce energy.”
“We took a closer look at how catechins act in the nematode worm Caenorhabditis elegans and came to a different, seemingly paradoxical conclusion: rather than suppressing oxidative stress, green tea catechins promote it.”
In their experiments, the researchers found that applying the green tea catechins EGCG and ECG at a low dose extends the lifespan of Caenorhabditis elegans.
The long-term effects also included reduced fat content in the nematodes after 5 days of catechin treatment.
“ECG and EGCG initially increase oxidative stress in the short term, but that this has the subsequent effect of increasing the defensive capabilities of the cells and the organism,” they explained.
“As a result, the catechins in green tea led to longer life and greater fitness in nematodes that were fed to them.”
“That means green tea catechins aren’t in fact antioxidants, but rather pro-oxidants that improve the organism’s ability to defend itself, similar to a vaccination,” Dr. Ristow noted.
“However, this increase in defensive capability manifests not through the immune system, but rather by activating genes that produce certain enzymes such as superoxide dismutase and catalase.”
“It is these enzymes that inactivate the free radicals in the nematode; they are essentially endogenous antioxidants.”
“While the most catechins are to be found in Japanese varieties of green tea, other green teas also contain sufficient amounts of these polyphenols,” he said.
“Black tea, on the other hand, contains a much lower level of catechins, since these are largely destroyed by the fermentation process. That’s why green tea is preferable to black tea.”
The findings were published in the journal Aging.
J. Tian et al. 2021. Green tea catechins EGCG and ECG enhance the fitness and lifespan of Caenorhabditis elegans by complex I inhibition. Aging (Albany NY) 13 (19): 22629-22648; doi: 10.18632/aging.203597