Characterization of dietary melanoidins and evaluation of the cytotoxic activity against colon cancer cells

Emerging evidence from in vitro and in vivo studies suggested that the gastro-intestinal tract may be the key site for the biological action of food melanoidins. Recently, Vitaglione et al. reviewed the possible mechanisms by which coffee melanoidins may influence the risk of colorectal cancer development. In this work, we tested high molecular weight melanoidins (HMWM) extracted from different food sources for their cytotoxic activity against colon cancer cell lines. Water soluble HMWM were extracted by ultrafiltration (cut-off 10 kDa) from instant coffee, cocoa brew, dark beer and instant barley coffee. HMWM have been chemically characterized for their content in total polyphenols, protein, and polysaccharides, antioxidant activity as well as their spectroscopic properties. These extracts were assessed using two colon cancer cell lines: Caco-2 and SW480. Cytotoxic activity was assayed by MTT and data are presented as the dose that inhibited 50% control growth (IC50). All of the assessed HMWM were cytotoxic against Caco-2 cell line. Coffee HMWM were the most effective (IC50 of 1042 and 857 µg/mL after 24 and 48h of treatment, respectively) followed by dark beer, barley coffee and cocoa HMWM. Meanwhile, they are less effective against SW480 with coffee HMWM that were the most effective (IC50 of 2038 µg/mL after 48h) followed by cocoa, dark beer and barley coffee. Considering that the colon accumulates its content over at least 24h in a maximum volume of 2 litres, and that the daily intake of coffee melanoidins range between 0.5 and 2.0 g , it is possible to calculate a hypothetical concentration of coffee melanoidins in the colon between 0.25 and 1 mg/mL, which are values comparable to the IC50 for the cytotoxic activity against colon cancer cells