Abstract:
Polyphenolic fractions in tea are potent bio active molecules with health benefits including potential anticancer properties. However, the mechanism of action of tea as an anticancer or chemo-preventive agent is poorly understood, with no information on black tea and purple tea. The polyphenolic composition of 25 different types of Kenyan tea was determined using the High Performance Liquid Chromatography (HPLC) and the Folins Ciocalteus methods. Total polyphenols (TP), Total catechins (TC), individual catechins and antioxidant activity (AA) were significantly (P<0.05) different among tea varieties, with green tea having the highest levels of TP. In vitro bioassay carried out using 2, 2’-diphenyl picryl hydrazyl radical (DPPH) showed that Epigallocatechin gallate (EGCG) was the most potent catechin in antioxidant activity (r=0.968***). Black tea contained high levels of theaflavins (TFs) and thearubigins (TRs) (2.072% to l7.l2%), respectively which accounted for most of the antioxidant potential in this type of tea product (r=O.803*** and r=0.859***). These results suggest that conversion of catechins during black tea processing did not affect the free-radical potency of black tea. Results on Ames test based on the Salmonella typhimurium tester strain obtained showed that tea had no toxicity or mutagenic activity at a concentration of 20% (W/v), unlike the mutagen sodium azide. Tea extracts had a significant (P<0.05) antimutagenic activity with percent inhibition of 65%, 38% and 19.17% for green, purple and black tea, respectively. Further, in virro assays were carried out on 4T1 cancer cell line to determine the effect of tea on cancer cell growth and proliferation. Results obtained revealed that green tea had the highest inhibition on 4T I cells proliferation at a concentration of IC50 =l3.l2ug/ml. Further analysis of the 4T] cancer cell line treated with green, black and purple teas using 454 pyrosequencing generated 425,696 reads with an input mean length of 286.54. Trimmed sequences were imported on a CLC genomic workbench V7.03 and annotated on a reference mouse genome (Mus rnusculus strain C5 7BL/6.1). Results revealed a differential expression of apoptosis related genes in the transcriptome. Casp8, Casp9, Casp3, Casp6, Casp8AP2, Aifml, Aifm2 and Apoptl genes were significantly up regulated indicating the process of apoptosis was initiated and executed. These findings on caspases offer valuable information on the mechanism of tea as an anticancer agent. This demonstration of 4T1 cancer cell growth
