Autophagy-induced cell death by aqueous and polyphenol-enriched extracts of honeybush (Cyclopia spp.) in liver and colon cancer cells

Abstract

The anti-cancer potential of Cyclopia species (honeybush) has been demonstrated in several models. The present study investigated the effects of aqueous and polyphenol-enriched (PE) extracts of C. subternata and C. genistoides, as well as mangiferin and hesperidin, on different cell growth parameters in human liver (HepG2) and colon (HT-29) cancer cells. Mangiferin and hesperidin were most abundant in C. genistoides and C. subternata, respectively. Cyclopia subternata extracts had the highest ferric-reducing antioxidant capacity. Following exposure of the cells to the extracts and compounds, cell viability, proliferation, and death (apoptosis and autophagy) were determined. Cyclopia subternata extracts reduced cell viability and inhibited cell proliferation the most, associated with depletion of ATP. In HepG2 cells, the PE extracts were less effective than the aqueous extracts in reducing cell viability but more effective in inhibiting cell proliferation. Despite disrupting cell growth, none of the extracts induced apoptosis. The aqueous extracts affected autophagy in both cancer cells. Disruption of mitochondrial membrane integrity by the different extracts, presumably via polyphenol/iron interactions, is postulated to be involved; however, mangiferin and hesperidin had no effect, suggesting that other polyphenols and/or complex interactions between compounds are likely responsible for the differential cytotoxic and/or cytoprotective effects of the extracts.