Phytochemical Contents and Anti-Colon Cancer Activities of Macadamia integrifolia Maiden & Betche Leaves and Husks Extracts

The macadamia (Macadamia integrifolia Maiden & Betche, Proteaceae Family) leaves and husks were the by-products from macadamia nut production which have few reports on the phytochemicals and pharmacological activities. This study aimed to investigate the possibility of using these by-products in drug discovery by examining their phytochemicals contents, as well as their anti-colon cancer activities. Dry macadamia leaves and husks were extracted and fractionated to obtain the crude extracts (EtOH), dichloromethane (DCM), ethyl acetate (EtOAc) and water fractions. Colorimetric methods were used to determine the total amounts of phytochemicals. The anti-colon cancer activities of the extracts against human colorectal carcinoma (HCT116) cell line were assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results showed that each gram of the samples contained total phenolics between 2.9-12.9 mg equivalent to gallic acid, total flavonoids 30.1-89.7 mg equivalent to rutin, and total triterpenoids 228.4-640.9 mg equivalent to ursolic acid. The DCM and EtOAc fractions of the husks exhibited the highest anti-colon cancer activity, with half maximal inhibitory concentrations (IC50) of 39.1 ± 4.3 and 56.9 ± 15.0 µg/mL, respectively. The EtOAc and water fractions of the leaves had IC50 values of 130.9 ± 17.4 and 127.8 ± 7.9 µg/mL, respectively. The IC50 values of other samples were greater than 200 µg/mL, while the IC50 of sorafenib, a positive control, was 5.95 ± 1.26 µg/mL. In conclusion, the leaves and husks of macadamia contained high amounts of several phytochemicals and exhibited anti-colon cancer activity against HCT116. These findings suggested that the extracts from these wastes may have potential in the discovery of anticancer agent research. Keywords: Macadamia integrifolia, Leaf, Husk, Colon cancer, Phytochemical