Colon-available dietary melanoidins exhibit cytotoxic activity on human colon adenocarcinoma cell lines

Introduction Emerging evidence from in vitro and in vivo studies suggested that the gastro-intestinal tract might be the key site for the biological action of food melanoidins [1]. Recently, Vitaglione et al. [2] reviewed the possible mechanisms by which coffee melanoidins may influence the risk of colorectal cancer development. In this work, we tested the water-soluble high molecular weight melanoidins (HMWM) obtained from different food sources for their cytotoxic activity against colon cancer cell lines. Method HMWM were obtained by ultrafiltration (cut-off 10 kDa) from instant coffee, cocoa brew, dark beer and instant barley coffee beverages [2]. HMWM have been chemically characterized for their content in total polyphenols, protein, and polysaccharides as well as their spectroscopic properties. The value of Kmix 420nm (defined as the absorption at 420nm of a solution of HMWM at a concentration of 1 g/L) provides information on the relative amount of melanoidins (Kmix 420nm) respect to other compounds found in the HMWM of beverages. Cytotoxic activity against two colon cancer cell lines (Caco-2 and SW480) was assayed by MTT assay. HMWM obtained from the above beverages submitted to in vitro gastro-intestinal digestion [3], were subjected to the same chemical analysis and assayed for their cytotoxic activity. Results / Discussion / Conclusion Barley coffee had the highest HMWM content (83.3g/100g of dry matter) followed by coffee (34.4g/100g of dry matter), cocoa (28.1g/100g of dry matter) and dark beer (20.0g/100g of dry matter). The HMWM of coffee had the highest Kmix 420nm value, suggesting that this fraction is relatively rich in melanoidins. On the contrary, despite the highest content in HMWM, barley coffee was the sample with the lowest melanoidins content. Protein content of HMWM ranged from 6.1% (dark beer) to 10.6% (coffee) whereas polysaccharides content ranged from 42% (dark beer) to 61% (cocoa). Cocoa and coffee HMWM had the highest phenolic content (6 and 12%, respectively). The in vitro digestion caused a general decrease in the polysaccharide and protein content of all the analysed HMWM because of the action of amylolytic and proteolytic enzymes. The analysis of the content of polyphenols showed a decrease in these components as a result of the digestion. On the contrary, the in vitro digestion caused an increase in the Kmix 420nm of all the HMWM investigated suggesting that this process resulted in an enrichment in melanoidins. The effect of HMWM on the human colon adenocarcinoma Caco-2 and SW480 cell cultures was investigated. Un-digested HMWM had no significant cytotoxic effect against both the cell lines. However, the in vitro digestion greatly increased the cytotoxic activity of HMWM against both the cell lines. Coffee HMWM were the most active against Caco-2 cells whereas cocoa HMWM were found to be most active against SW480 cells. Considering that the colon accumulates its content over at least 24 h in a maximum volume of 2 l, it is possible to estimate the concentrations of HMWM reaching daily the colon with diet according to the different food matrices [1]. Data showed that, the consumption of coffee, cocoa and barley coffee beverages may result in intestinal concentrations of HMWM, which are cytotoxic against Caco-2 and SW480 cell lines.