Hyperpigmentation disorders are prevalent and distressing conditions characterized by the excessive secretion of melanin in the epidermis and/or dermis. Among these, post-inflammatory hyperpigmentation (PIH), which involves skin darkening resulting from inflammation and subsequent activation of melanogenesis by inflammatory mediators, represents a significant cosmetic concern, often exacerbated by ultraviolet (UV) radiation and prolonged sun exposure.
The need for novel ingredients is driven by the limitations of conventional cosmetic agents used for PIH, such as retinoids, corticosteroids, arbutin, salicylic acid, and vitamin C derivatives. While these agents exhibit efficacy, they often pose challenges, including the risk of irritant dermatitis, epidermal atrophy, telangiectasia, or even paradoxical hyperpigmentation. Consequently, there is an ongoing research frontier focusing on ingredients that possess dual effects of both anti-melanogenesis and PIH prevention, particularly those derived from plant extracts.
Dark tea (DTE), a traditional fermented tea, has gained attention due to its rich composition of bioactive components, including tea polyphenols and theaflavins, which are associated with various health benefits such as antioxidation. Given the natural, safe, and mild characteristics sought in cosmetic raw materials, DTE was considered a highly promising candidate for investigating its potential skin-brightening efficacy, specifically through anti-melanogenesis and PIH amelioration.
Methods
The investigation employed in vitro cell experiments to evaluate the efficacy of dark tea extract (DTE). The anti-melanogenesis effect was assessed by examining melanin content and tyrosinase activity in $\alpha$-MSH-stimulated B16 melanoma cells. To model PIH, DTE’s impact on the secretion of inflammatory factors (IL-1$\alpha$ and IL-1$\beta$) and paracrine melanogenic factors (ET-1, $\alpha$-MSH, and bFGF) was determined using ELISA in UVB-irradiated HaCaT keratinocytes. The mechanistic studies relied on quantitative real-time polymerase chain reaction (RT-PCR) and Western Blot analyses to clarify the involvement of the $\alpha$-MSH/MC1R/MITF and p38 MAPK/Nrf2/HO-1 signaling pathways.
Key Findings
• Anti-Melanogenesis Effect: Dark tea extract (DTE) significantly inhibited melanin content and tyrosinase (TYR) activity in B16 cells. Specifically, a concentration of 7.5 µL/mL DTE significantly decreased tyrosinase activity by 46% and melanin content by 60%.
• PIH Inhibition via Inflammatory Factors: DTE effectively suppressed the expression and secretion of key inflammatory factors (IL-1$\alpha$ and IL-1$\beta$) in UVB-irradiated HaCaT cells, which were used to model PIH. At 7.5 µL/mL, DTE reduced IL-1$\alpha$ and IL-1$\beta$ generation by 61% and 78%, respectively.
• Inhibition of Paracrine Melanogenic Factors: DTE progressively suppressed the expression levels of paracrine melanogenic factors (ET-1, $\alpha$-MSH, and bFGF) induced by UVB irradiation in HaCaT cells.
• Mechanism of PIH Inhibition: The PIH inhibition effect was exerted by DTE through the downregulation of the p38 MAPK pathway and the upregulation of the Nrf2/HO-1 signaling pathway in HaCaT cells, mitigating UVB-induced oxidative stress and reducing inflammatory factor release.
• Mechanism of Anti-Melanogenesis: DTE inhibited melanogenesis by downregulating the $\alpha$-MSH/MC1R/MITF signaling pathway and its downstream multiple targets, specifically the melanin-producing markers: TYR, TYRP-1, and TYRP-2.
This study successfully demonstrated that Dark Tea Extract (DTE), which is enriched with polyphenolic constituents, exhibits a dual efficacy as a skin-brightening agent. The novelty of this research lies in validating DTE’s ability to concurrently suppress melanogenesis through multi-target actions (MC1R, MITF, TYR, TYRP-1, and TYRP-2) and prevent darkening by inhibiting PIH. By modulating the p38 MAPK/Nrf2/HO-1 signaling pathway, DTE prevents pigmentation triggers, while simultaneously interrupting melanin biosynthesis pathways, demonstrating a comprehensive approach to treating pigmentation disorders. These findings suggest that DTE, possessing such a multi-target profile and dual action, represents a promising natural active ingredient for the future development of comprehensive skin-brightening formulations and agents for the restoration of pigmentation disorder stabilization.
Link to the study: https://www.mdpi.com/2079-9284/12/5/210
