Research Projects

Chemopreventive potential of Rooibos in skin carcinogenesis – Prof Wentzel Gelderblom

Chemopreventive potential of Rooibos in skin carcinogenesis – Prof Wentzel Gelderblom

Prof Wentzel Gelderblom

Cape Peninsula University of Technology, Institute of Biomedical and Microbial Biotechnology

Email: GelderblomW@cput.ac.za

Title of the project

Chemopreventive potential of Rooibos in skin carcinogenesis

Project description

Chronic inflammation has been implicated to play a key role in the promotion stage of skin carcinogenesis and is therefore recognized as a major risk factor. An important research focus over the last two decades has been the use of natural anti-inflammatory products which are able to reverse skin cancer promotion. Rooibos (Aspalathus linearis), a South African indigenous herbal tea, is becoming more and more popular with consumers and researchers worldwide. Its antioxidant and antimutagenic properties are well established and animal models for skin, liver and oesophageal cancer have shown anticancer effects.

The anti-inflammatory properties of aqueous and methanol extracts of rooibos were investigated in UVB-irradiated skin keratinocyte (HaCaT) and lipopolysaccharide (LPS)/macrophage inflammatory cell models in order to further characterize the cancer preventive mechanisms in skin. The project was aimed to characterize possible mechanisms underlying the chemopreventive properties of rooibos extracts and chromatographic fractions that are important in the prevention of cancer promotion in skin carcinogenesis. These include key target processes of inflammation, cell proliferative and apoptosis associated with skin carcinogenesis.

Non-scientific Report

Chronic inflammation is a recognized risk factor for epithelial carcinogenesis, including the skin epithelium. When provoked by stimuli such as ultraviolet irradiation, keratinocytes participate in immune responses by releasing a complex array of pro-inflammatory factors or cytokines. This in turn, allows the keratinocytes to recruit inflammatory cells and regulate their behaviour. Interleukin-1alpha (IL-1α) and TNF-alpha, are termed primary cytokines because they activate a number of pro-inflammatory proteins that are necessary to resolve the complex inflammation process. This study focused on two cell types that are relevant to skin carcinogenesis – (i) keratinocytes that are the most abundant cell type in the epidermis and (ii) macrophages that are immune cells coordinating inflammatory responses. Cell culture models were developed where herbal tea extracts and chromatographic fractions were tested before and after UVB irradiation in keratinocytes and before and during stimulation of inflammatory responses in macrophages by lipopolysaccharide (LPS). UVB irradiation increased the content of the pro-inflammatory protein IL-1α and caused programmed cell death in keratinocytes in culture. Rooibos extracts increase the number of cells that undergo programmed cell death in a post-exposure UVB model, which presumably reduces the number of genetically damaged and/or potentially pro-inflammatory cells, thereby modifying a key process involved in skin cancer development. However, the current model only reflects limited information about the complex mechanisms involved, therefore further investigation is required to characterize the underlying mechanisms regarding the benefit of this effect.

The anti-inflammatory effects of unfermented, fermented rooibos extracts and chromatographic fractions of an unfermented methanol extract (X1 to X5) were also investigated in the UVB/HaCaT inflammation model monitoring IL-1α production and cell growth regulatory responses as endpoints. In the absence of UVB exposure the methanol extracts and the flavonoid-enriched fractions, X3 and X-4, increased IL-1α associated with a decrease in cell viability and increase in apoptosis, suggestive of a pro-inflammatory effect. The aqueous extracts and the polar fraction X-2 had the opposite effect by decreasing IL-1α with minor effects on cell viability and apoptosis at low concentrations, suggesting an anti-inflammatory response. In the presence of UVB all the extracts and most of the column fractions resulted in a decrease in IL-1α accumulation in comparison to the control, with the methanol unfermented extract and flavonoid enriched chromatographic fractions being the most active. Therefore, rooibos may aid the removal of IL-1α indirectly presumably by inducing cell death although a critical balance appear to exist in the type of cell death, e.g. via apoptosis or via necrosis where the cytokines is released and should be avoided

Pre-exposure of HaCaT keratinocytes to rooibos extracts exhibited an anti-inflammatory response without adversely affect the cell growth parameters likely to protect against oxidative stress affected by UVB-induced irradiation. The anti-inflammatory activity in this model may be due to the anti-oxidant properties of polyphenolic constituents inhibiting the multiple pathways leading to the activation of activator protein-1 (AP-1) and nuclear factor kappa B (NF-κB) pathways governing the inflammatory cytokine responses which are currently under investigation.

All the extracts and chromatographic fractions decreased TNF-α release in the LPS/macrophage inflammatory cell model with minor effects on the cell growth parameters. The aqueous fermented extract and the most polar chromatographic fraction were the most active in decreasing TNF-α while pre-exposure prior to LPS introduction was found to be the most effective. The flavonoid enriched column fractions reduced the excretion of TNF-α, although cell viability was decreased and apoptosis was increased at higher concentrations. The LPS/macrophage inflammatory model seems to be more resistant to the pro-oxidant effects of the rooibos extracts and chromatographic enriched flavonoid fractions and provide an ideal model to further characterize the anti-inflammatory properties of rooibos.

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