In vitro cell specific effects of rooibos (Aspalathus linearis) and the active compound aspalathin on malignant and benign prostate cell lines

Rooibos (A. linearis) may promote oxidative stress in malignant prostate cells through increased reactive oxygen species (ROS) production but may protect normal prostate cells from ROS induced stress. To test this hypothesis, malignant LNCaP and benign RWPE-1 prostate cells were exposed to aqueous solutions of 125 - 50 000 µg/mL fermented rooibos, unfermented rooibos or aspalathin for 72-hours. ROS quantification using CM-H2DCFDA fluorophore produced significantly (P < 0.05) increased ROS levels in malignant (LNCaP) prostate cells but not in benign (RWPE-1) prostate cells. The MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay using mitochondrial dehydrogenase activity as a function of cell viability showed a concentration-dependent, significant (P < 0.05) decrease in viability of LNCaP cells following treatment with 5 000 - 50 000 µg/mL unfermented rooibos whilst in RWPE-1, viability was maintained at all concentrations used. The apoptotic assay using annexin V showed significantly (P < 0.05) increased percentage of apoptotic and necrotic LNCaP cells, respectively compared with their respective negative controls. In contrast, benign RWPE-1 cells produced a significant (P < 0.05) drop in the percentage of apoptotic and necrotic cells, respectively compared to their specific negative controls. Fermented rooibos, unfermented rooibos, and aspalathin respectively, significantly (P < 0.05) reduced the total serum prostate specific antigen (PSA) in malignant LNCaP prostate cells whereas in benign RWPE-1 prostate cells, the total serum PSA level was comparable to that of its specific negative control. This study suggests cytotoxic effects of unfermented rooibos on malignant LNCaP cells and protective effects on benign RWPE-1 cells against ROS induced stress. The decrease in total serum PSA seems to demonstrate possible therapeutic effects of A. linearis on malignant LNCaP prostate cells and possible maximum health benefits from total polyphenol content.