Cytoprotective and pro-apoptotic activities of native Australian herbs polyphenolic-rich extracts

Three commercially grown native herbs unique to Australia, Tasmannia pepper leaf (Tasmannia lanceolata R. Br., Winteracea; TPL), anise myrtle (Syzygium anisatum Vickery, Craven & Biffen, Myrtaceae; AM) and lemon myrtle (Backhousia citriodora F. Muell, Myrtaceae; LM) as well as a reference sample bay leaf (Laurus nobilis L., Lauraceae; BL) were examined for potential cytoprotective properties. All native herbs exhibited greater cellular antioxidant activity as measured by the cellular antioxidant activity (CAA) assay than bay leaf and reduced the hydrogen peroxide (H2O2) induced death of hepatocellular carcinoma (HepG2) cells by 25–50%. All herb extracts reduced the proliferation of colon (HT-29; IC50 = 0.75–1.39 mg/ml), stomach (AGS; IC50 = 0.59–1.88 mg/ml), bladder (BL13; IC50 = 0.56–1.12 mg/ml) and liver (HepG2; IC50 = 0.38–1.36 mg/ml) cancer cells. No significant reduction of cell viability of non-transformed colon (CCD-18Co; IC50 > 2.0 mg/ml) and mixed stomach and intestine (Hs 738.St/Int; IC50 > 2.0 mg/ml) cells was observed. Flow cytometry analysis and the results of the cytokinesis block micronucleus cytome (CBMNCyt) assay conducted with respectively, promyelocytic leukaemia (HL-60) and colon adenocarcinoma (HT-29) cells suggest an increase in apoptosis following treatment with the herb extracts. The occurrence of apoptotic cells coincided with an increase in caspase-3 enzyme activity. The results of the CBMNCyt assay suggested no direct DNA damage in colon adenocarcinoma (HT-29) cells as a result of treatment with all extracts, applied at final concentrations of 0.5 and 1.0 mg/ml.