Dark tea is a post-fermented tea native to many regions of China, including Yunnan, Hunan, Sichuan, and Guangxi provinces.
Although it is widely used in food and pharmaceutical products because of its properties, such as fat reduction, antioxidant, immunomodulatory, and anti-fatigue, its application in the cosmetics industry has rarely been reported.
A group of Chinese researchers extracted dark tea polysaccharide (DTP) to investigate its effects on stress-induced skin problems and its mechanism of action by modelling cortisone-induced lipid secretion in human HaCaT keratinocytes and SZ95 sebaceous gland cells.
The hypothalamic-pituitary-adrenal (HPA) axis is the main neuroendocrine system involved in stress regulation. Under stressful conditions, the central HPA and cutaneous HPA axes are activated, and stress hormones are released, accelerating sebaceous gland production and lipid secretion.
Excessive accumulation of cortisol has also been shown to inhibit the proliferation of keratin-forming cells and fibroblasts, thereby obstructing renewal of the stratum corneum and weakening the skin barrier function.
In this study, it was found that DTP at a concentration of 200μg/mL could inhibit the conversion of stress-mediated cortisol, possibly by inhibiting the expression of the HSD11B1 enzyme.
Furthermore, the results showed that DTP — at the same concentration — was able to reverse the elevation of lipid levels induced by cortisone in SZ95 sebocytes.
“These findings suggest that DTP has a significant stress-relieving effect and can alleviate skin oiliness caused by stress, providing a theoretical basis for the application of dark tea in cosmetics, especially in addressing stress-related skin problems,” the authors wrote.
High biological activity
Stress is a biochemical response triggered by environmental or external physical forces, which leads to changes in the physiological activities of the body.
If the stress response is inadequate or excessive, an overproduction of stress mediators may lead to a range of skin problems, such as skin barrier damage, acne, melanin deposition, skin ageing, and inflammation.
A high-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) investigation showed that the main monosaccharides in DTP are arabinose, galactose, glucose, galacturonic acid, and glucuronic acid in a molar ratio of about 1:1:2:1.8:0.3.
This indicates that DTP is an acidic polysaccharide, which usually has high biological activity and an ability to regulate human immunity.
In addition, DTP was found to have a high percentage of low-molecular-weight polysaccharides and water-soluble polysaccharides. This provided evidence for the origin of the stress-relieving effects of DTP.
“As stress evaluation in this study was conducted using skin cells, subsequent studies could validate the results on skin models and clinical trials to prove the efficacy of DTP and to advance the ingredient’s application in cosmetics,” said the authors.
“Effects and Stress-Relieving Mechanisms of Dark Tea Polysaccharide in Human HaCaT Keratinocytes and SZ95 Sebocytes”
Authors: Chang Gao, et al