You know that stuff those non-coffee drinkers drink? Yeah me neither. Well, it’s quite good for you and contains caffeine. Maybe it’s time for a change from coffee…tomorrow…I’ll switch tomorrow.
Three takeaways to tell your friends:
- Seven days of administering mice green tea polyphenols relieved depression symptoms as well as a popular antidepressant in mice.
- One day of green tea polyphenols administration failed to treat depression symptoms in mice.
- Seven days of green tea polyphenols, before a stressful situation, decreased the release of stress-inducing hormones in mice.
Depression continues to be a common problem amongst the general population. While there are many prescription drugs available to treat depression, patients can have a hard time finding the one that works for them. Patients who do not see improvements in their depressive symptoms following two prescription medications are considered to have Treatment-Resistant Depression (TRD). According to a 12-month analysis, approximately 31% of patients with depression have TRD(1). For this reason, extensive research has continued into alternative treatments for depression.
Today, we’re discussing a non-traditional seven-day alleviation of depressive symptoms in mice published by Zhu et al in Pharmacological Research(2). They examined the medicinal aspects of green tea leaves. Green tea is the fifth most popular non-alcoholic beverage in the world, according to TasteAtlas(3), and it is loaded with healthy compounds. These are known as polyphenols, a name for compounds that contain two or more (poly) aromatic rings (phenols). In chemistry, a phenol group is a six-sided carbon ring. Polyphenols are found in many natural products: tea, apples, berries, citrus, soybeans, grapes, flax seeds, and onions. Increasing polyphenols in the diet has been correlated with healthier outcomes: reduced death from cardiovascular disease and coronary heart disease, lower incidence of cancers, improved performance on cognitive tests, and reduced blood pressure(4).
In today’s article, the researchers extracted the polyphenol compounds from green tea. Over seven days, researchers injected the polyphenolic compounds into the mice through a feeding tube releasing the contents directly into the mouse stomach. The mice were either administered green tea polyphenols (GTP), a placebo, or venlafaxine. Venlafaxine is a popular antidepressant, used in this experiment as a positive control, so if GTPs have an antidepressant effect, then their results would be similar to venlafaxine.
The two behavioral tests used to examine mouse depressive behavior are the Tail Suspension Test (TST)(5) and the Forced Swim Test (FST)(6). The TST involves suspending a mouse 50cm above the ground from its tail and recording the time that it spends immobilized. Given the mouse is stuck there, it’s a measure of the animal’s willingness to fight to free itself. Similarly, the FST places a mouse in a 20cm diameter cylindrical pool of water for 6 minutes and records the amount of time the mouse spends immobilized. Again, the mouse has two choices, fight for survival or despair. The theme here is that the longer they fight to survive, the less depressed they are.
Following a seven-day treatment of GTPs, mice performed the TST and FST. Mice treated with GTPs spent significantly more time immobilized than placebo mice. Also, mice treated with GTPs spent a similar amount of time immobilized as mice treated with venlafaxine. To test that this result isn’t due to GTP affecting the movement of the mice, researchers ran a test for locomotor activity and found no differences in any treatment groups. These results suggest that a seven-day treatment of GTPs can offer antidepressant effects.
Mice treated with GTPs for only one day had no differences from placebo mice in time spent immobilized throughout the TST and the FST.
While testing to see if the locomotor activity test was creating a new stressor on the mice, they discovered something quite fascinating. They wanted to know if they needed to conduct the locomotor activity test at a different time to not stress the mice before the FST. To test the stress from the locomotor assessment, researchers measured stress hormones released in the bloodstream. Upon testing the hormone levels from each treatment group, they found significantly lower levels of stress hormones in the groups treated with GTPs, comparable to the venlafaxine group. Interestingly, this result was only observed in mice following a stressful event (the FST). Without a stressful event, the levels of stress hormones were consistent across all treatment groups.
Serendipity, my friends, serendipity. The polyphenols within green tea reduce depressive symptoms in mice AND decrease the stress response.
Time for me to start looking into the bioavailability of GTPs. See you on the other side, future tea lovers!
Experimental factors to consider…
There is controversy regarding these behavioral tasks, specifically the TST, but mice have repeatedly shown decreased time spent “giving up” following antidepressant administration.
REFERENCES
1) Zhdanava M, Pilon D, Ghelerter I, Chow W, Joshi K, Lefebvre P, et al. The Prevalence and National Burden of Treatment-Resistant Depression and Major Depressive Disorder in the United States. J Clin Psychiatry. 2021;82(2).
2) Zhu WL, Shi HS, Wei YM, Wang SJ, Sun CY, Ding ZB, et al. Green tea polyphenols produce antidepressant-like effects in adult mice. Pharmacol Res. 2012;65(1):74-80.
3) TasteAtlas. “Most Popular Non-Alcoholic Beverages in the World.” TasteAtlas, TasteAtlas, 19 Feb. 2023, https://www.tasteatlas.com/most-popular-non-alcoholic-beverages-in-the-world.
4) Stevenson DE, Hurst RD. Polyphenolic phytochemicals–just antioxidants or much more? Cell Mol Life Sci. 2007;64(22):2900-16.
5) Steru L, Chermat R, Thierry B, Simon P. The tail suspension test: a new method for screening antidepressants in mice. Psychopharmacology (Berl). 1985;85(3):367-70.
6) Yankelevitch-Yahav R, Franko M, Huly A, Doron R. The forced swim test as a model of depressive-like behavior. J Vis Exp. 2015(97).
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