Magister Scientiae (Medical Bioscience) - MSc(MBS) / The prostate is prone to three pathological processes that include inflammation, benign prostate hyperplasia (BPH) and tumors. According to the center for Disease and Control 1999-2012 report, prostate cancer is the second leading cause of death in the United States. Scientific evidence suggests that up to 30% of men in the general population aged from 50 years and above, irrespective of geographic origin, have foci of prostate neoplastic growth. Unbalanced ROS production and a dysregulated antioxidant defence system have been implicated in prostate cancer development. The transformation of a normal cell into cancer takes a very long period. This observation provides the advantage of using nutraceuticals to prevent, arrest or reverse the cellular and molecular processes of carcinogenesis. Based on scientifically observed positive health roles of green tea (Cameli sinensis) and rooibos (Aspalathus linearis) on major diseases like atherosclerosis, hepatitis and certain types of cancer, this thesis evaluated the effects of these two teas on benign (RPWE 1) and malignant (LNCaP) prostate cells. This was done through the quantification of reactive oxygen species (ROS) using a fluorescence dye 5,6 CM-H2DCFDA, total prostate specific antigen (PSA) levels using a PSA ELISA kit, cell viability using the MTT assay, apoptosis using Tali annexin V stain and cell imaging studies using a Zeiss axiovert 200M inverted fluorescence microscope. Statistical analysis was done using graphpad prism. The findings of this study show that aqueous extracts of green and black tea, fermented and unfermented rooibos and their active compounds epigallocatechin gallate (EGCG) and aspalatin, respectively, are cytotoxic in malignant (LNCaP) prostate cells but exert protective effects in benign (RPWE 1) prostate cells. This thesis implicates the pro-oxidant and anti-oxidant properties of the plant extracts, respectively, for the above mentioned effects. In this regard, tea and rooibos promoted ROS production in malignant (LNCaP) prostate cells, which subsequently promoted cell death of the malignant cells through apoptosis and necrosis. Further to this, tea and rooibos used in this thesis, protected normal prostate cells from the adverse effects of ROS. In this regard, fluorescence microscope photographs showed RPWE 1 cells with low DCF fluorescence compared to the malignant prostate cells. Low magnification light microscope photographs showed RPWE 1 cells with flat polygonal shapes and increased adherence both at low and high concentrations of tea and rooibos. On the contrary, high concentrations of tea and rooibos on malignant (LNCaP) prostate cells induced stress, which made the cells attain irregular shapes and as the stress levels increased, cells became detached and appeared dead. Flow cytometry confirmed the presence of apoptotic and necrotic cell in malignant (LNCaP) prostate cells. In this thesis, EGCG and aspalathin were responsible for the high rates of apoptosis observed whereas green tea and unfermented rooibos induced the highest rate of necrosis. Further to this, tea and rooibos and the main active compounds EGCG and aspalathin, respectively, significantly promoted the reduction of total serum prostate specific antigen (PSA) in malignant prostate cells. In normal prostate cells, these plant extracts maintained the total serum PSA at its basal physiological level. In this thesis, to the best of our knowledge, we report for the first time the cell-specific effects of fermented rooibos, unfermented rooibos and their main active component aspalathin, on prostate cancer cells. We showed that rooibos and aspalathin exert pro-oxidant effects on malignant LNCaP cells and anti-oxidant effects on benign RPWE 1 cells. In conclusion, tea (C. sinensis) and rooibos (A. linearis) and their respective main active compounds, epigallocatechin gallate and aspalathin, are cytotoxic to malignant prostate cells whereas in normal prostate cells, they have protective effects against ROS induced stress. The pro-oxidant and anti-oxidant effects are responsible for the aforementioned effects respectively. The decrease in total serum PSA demonstrate the strong therapeutic effects that tea and rooibos have on malignant (LNCaP) prostate cells. / Malawi Government: Department of Human Resources Development and Management