In vitrofermented nuts exhibit chemopreventive effects in HT29 colon cancer cells

Abstract

It is proven that nuts contain essential macro-and micronutrients, e.g. fatty acids, vitamins and dietary fibre (DF). Fermentation of DF by the gut microflora results in the formation of SCFA which are recognised for their chemopreventive potential, especially by influencing cell growth. However, little is known about cellular response to complex fermentation samples of nuts. Therefore, we prepared and analysed (pH, SCFA, bile acids, tocopherol, antioxidant capacity) fermentation supernatant (fs) fractions of nuts (almonds, macadamias, hazelnuts, pistachios, walnuts) after in vitro fermentation and determined their effects on growth of HT29 cells as well as their genotoxic/anti-genotoxic potential. The fermented nut samples contained 2-to 3-fold higher amounts of SCFA than the faeces control, but considerable reduced levels of bile acids. While most of the investigated native nuts comprised relatively high amounts of tocopherol (a-tocopherol in almonds and hazelnuts and g-and d-tocopherol in pistachios and walnuts), rather low concentrations were found in the fs. All nut extracts and nut fs showed a strong antioxidant potential. Furthermore, all fs, except the fs pistachio, reduced growth of HT29 cells significantly. DNA damage induced by H 2 O 2 was significantly reduced by the fs of walnuts after 15 min co-incubation of HT29 cells. In conclusion, this is the first study which presents the chemopreventive effects (reduction of tumour-promoting desoxycholic acid, rise in chemopreventive SCFA, protection against oxidative stress) of different nuts after in vitro digestion and fermentation, and shows the potential importance of nuts in the prevention of colon cancer.

In vitro fermentation of nuts results in the formation of butyrate and c9,t11 conjugated linoleic acid as chemopreventive metabolites

“…These results are in line with former studies which have shown that the fermentation of dietary fiber or fiber-rich foods results in the formation of SCFA and concurrently in lower pH values [31,32]. Similar results have also been obtained by Lux et al [22], who applied different types of nuts to an in vitro simulated digestion. The marginal differences between the SCFA values in our study compared to those by Lux et al can be explained by the used feces matrix, which was obtained from different donors.…”

“…In addition, the SCFA-mediated lowering of pH values in the FS might lead to reduced solubility of secondary BA as well as a reduction in 7α-dehydroxylase activity, which catalyzes the conversion of primary into secondary BA [50]. The results of the present study are in line with former studies, which have also shown a reduction in secondary BA concentrations upon in vitro fermentation of different dietary fiber sources [22,24,31,32].…”

“…The digestion of nuts was performed using an in vitro simulation of the gastrointestinal passage as described previously [23,24] with slight modifications [22]. Briefly, 2 g of ground nuts (raw nuts and nuts roasted with five different conditions) were reconstituted with anaerobic potassium phosphate buffer (0.1 M, pH 7.0), incubated with α-amylase (17.4 U/sample from a 1000 U/ml stock solution in 20 mM-NaH 2 PO 4 ) and 0.85 % NaCl for 5 min and subsequently for 2 h with pepsin at 37 °C (1.11 mg in 0.94 mL 20 mM HCl, pH 2.0).…”

“…Until now, there are only a few studies which elucidate the formation of fermentation end-products with possible chemopreventive properties upon digestion and fermentation of nuts [22]. There is also no sufficient information, how the human fecal microbiota metabolizes PUFA (e.g., LA) from a PUFA-rich source such as nuts or whether these FA are subjected to conversion to CLA.…”

Influence of roasting on the chemopreventive potential of macadamia nuts

“…Butyrate could therefore be mainly responsible for growth inhibitory effects of macadamia FS observed in the present study. These results are in line with other studies demonstrating growth inhibition of LT97 colon adenoma [18] or HT29 colon carcinoma cells [28] by FS obtained from different raw nut varieties including macadamia. Growth inhibition of colon adenoma or cancer cells could also be shown for FS obtained from other dietary fiber rich sources such as bread [29] or wheat aleurone [30], respectively.…”