Modulation of UVB-induced inflammation and oxidative stress by unfermented rooibos and honeybush aqueous extracts: A comparative study
Date
2024-12
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Publisher
Stellenbosch University
Abstract
Exposure to Ultraviolet B (UVB) radiation induces various biological responses that may contribute to skin cancer development. Natural compounds such as tea polyphenols have demonstrated protective effects against UVB-induced damage. Rooibos (Aspalathus linearis) and honeybush (Cyclopia spp.) are two South African herbal plants that have gained attention for their potential health benefits. Rooibos has recently been registered by the European Commission in its lists of Protected Designations of Origin (PDO) and Protected Geographical Indication (PGI) and therefore has protected status as it is only allowed to be grown in the Cederberg area of the Western Cape, South Africa. The current study explores the preventive effects of unfermented rooibos and honeybush herbal tea aqueous extracts on oxidative stress, inflammation and phospholipid alterations in HaCaT human keratinocytes exposed to UVB. The study utilises a pre-exposure HaCaT model, where cells are treated with tea extracts prior to UVB exposure. An array of assays and techniques were utilized to determine the antioxidant and anti-inflammatory effects on specific cytokines, genes and proteins involved in these processes, as well as ion mobility-mass spectrometry (IM-MS) to investigate effects on the major keratinocyte phospholipids. HPLC analysis showed the presence of the dihydrochalcones, aspalathin and nothofagin, the flavones, isoorientin and orientin, as well as the flavonols, rutin, isoquercitrin, and hyperoside in the rooibos extract. The major compounds found in honeybush extract included the xanthones, mangiferin and iso-mangiferin, and the flavanone, hesperidin. Rooibos demonstrated superior free radical scavenging activity against ABTS and DPPH, antioxidant capacity (ORAC), ferric iron reducing potential (FRAP) and greater inhibition of iron-induced peroxidation (LPO) compared to honeybush. Both teas also exhibited cell-based antioxidant properties by increasing glutathione (GSH) levels, and the increase in GPX1 and CAT expression, while only rooibos upregulated Nrf2 expression. Microarray analysis confirmed the antioxidant activity of both teas in the increased expression of GCLM, GPX and PRDX. The results indicate that honeybush reduces UVB-induced interleukin (IL)-1α accumulation and IL-6 secretion, while both teas decrease IL-8 secretion and NF-κB activation, demonstrating the anti-inflammatory effect of rooibos and honeybush. The treatment of keratinocytes with rooibos and honeybush alone did not affect the levels of any of the lipid species identified in the current study. However, exposure of the cells to UVB significantly decreased the levels of all of evaluated phospholipids. Neither rooibos nor honeybush were able to significantly counteract this decrease in phospholipid levels, with honeybush even further decreasing PC 34:1, PC 36:1, PC 36:4, PE 38:4 and SM 34:1 levels. Rooibos and honeybush contain completely different polyphenol profiles, which is reflected in their activities, with rooibos displaying more antioxidant activity while honeybush has greater anti-inflammatory activity. This research has the potential to inform the production of sunscreen products utilizing natural extracts to protect against the harmful effects of UVB exposure.