Comparative in vitro study of the anti-cancer effect of apricot and peach kernel extracts on human colon cancer cells
Amygdalin, a controversial anti-cancer agent, is a cyanogenic glycoside plant compound found in apricot and peach kernels. Both amygdalin and its patented form, Laetrile®, have been promoted and sold as "vitamin B-17", although neither compound is a vitamin. No consensus on the efficacy of amygdalin regarding the treatment of different cancers has been reached. Cancer is now the third leading cause of death worldwide. More than 7.6 million deaths were estimated to have occurred in 2007 and by 2030 it is projected to increase to 17 million cancer deaths per year. Cancers of the lung, breast, colon/rectum, liver and prostate are no longer largely confined to Western industrialized countries but are among the most common cancers worldwide (Thun et al. 2010). In South Africa it is estimated that one in every four males and one in every five females will be affected by a cancer diagnosis in their lifetime. The most common cancers in males are prostrate, lung, oesophagus, bladder and colorectal and in females they are cervix, breast, colorectal, oesophagus and lung (Haggar & Boushey 2009). Colon cancer is one of the most prevalent cancers worldwide, especially in western societies and is nutrition dependent (Klenow et al. 2009). It is one of the leading causes of death in both men and women in industrialised western countries. Colon cancer development involves both hereditary factors and lifestyle factors which include absence of physical exercise, unbalanced nutrition and long term smoking (Forman et al. 2004; Heavey et al. 2004). Colon cancer is traditionally treated by the resection of the colon, chemotherapy, radium therapy, and pharmaceutical hormonal drugs (Willson et al. 1987; Padussis et al. 2004)). Epidemiological studies supports evidence that colon cancer is preventable by adjusting the diet (Forman et al. 2004) and a protective effect is attributable to polyphenols and foods such as fruits and vegetables (Araújo et al. 2011). It was reported by Ruan et al. (2006) that the addition of Chinese Herbal Medicine in conjunction with chemotherapy notonly raised the efficacy of the chemotherapeutic drug, but also reduced the toxic side-effects. The aim of this research was to carry out a comparative in vitro study of the anti-tumour effect of the Chinese , South African and Turkish apricot (Xing ren / Armeniacea Semen) and Chinese and South African peach (Tao ren / Persica Semen) kernel extracts on the HT-29 colon cancer cell line.All the extracts significantly reduced cell viability and inhibited proliferation in the HT-29 cancer cells after 24 hours with the lipophilic and total fractions of CAK being the most effective. After 72 hours, it is clear that the inhibitory effects have been abolished and replaced by a stimulatory effect as the cell viability is higher in the treated cultures than the untreated controls. Results show that the total and the hydrophilic fractions of all the kernels increased cell viability more than the lipophilic fractions. It cannot be said with certainty that it was the amygdalin metabolite cyanide that affected the cell viability or induced apoptosis on its own. If hydrolysis of amygdalin indeed happened and cyanide was produced, it would affect the cells by shutting down aerobic respiration. Since cancer cells have more β- glucosidases and less rhodanese than normal cells, it is a possibility that the HT-29 cancer cells had some rhodanese to convert cyanide into a relatively harmless compound thiocyanate. It could be that in vitro this conversion, in light of the low enzyme levels in the HT-29 cancer cells, happened slowly and that the effect was only seen after 48 hour. However, this does not explain the overall inhibition even by the lipophilic fractions that should not contain any amygdalin or the eventual stimulatory effect, observed from 48 hour onwards.The S phase block observed, was mostly seen after 24 hour exposure to organic extractions, with the SAK showing 86% of cells in the S phase in contrast to the aqueous extractions which only slightly increased the S phase fraction. This could indicate that synergistic and/or additive effects between polyphenolic compounds may also be responsible for the reduction of cell viability, proliferation and apoptosis. All the kernels and the various fractions affected cell viability and to an extent cell cycle progression, but more studies is needed to establish the most effective kernel and specific fraction or signature active component. Inhibition of cell viability and proliferation and the induction of apoptosis could be an important preventive approach in chemoprevention. Understanding how dietary components regulate proliferation and cell survival could play a critical role in development of new enriched agents that can prevent and treat cancer with reduced risk of toxicity.