Factors Affecting Cellular Uptake of Anthocyanins: The Role of pH, Glucose and Anthocyanin Structure

Anthocyanins have poor bioavailability, but the factors affecting this remain unclear. Uptake into cells could impact the bioavailability; therefore, understanding factors affecting anthocyanin uptake is pivotal to improve their bioavailability and reveal the mechanism for their uptake. This study aimed to investigate the effect of anthocyanin structure, pH and glucose on the uptake of anthocyanins by Caco-2 cells. Anthocyanin extract from strawberry and red grape at 10 or 20 µM was added to Caco-2 cells. Anthocyanin toxicity to the cells was firstly examined to ensure the same cell viability. The uptake was carried out at pH 7 and 6.5 to evaluate the effect of pH. Glucose (1 mM) was used to investigate its effect. The results show that anthocyanins toxicity was dependent on the concentration and length of exposure. Anthocyanin uptake was concentration-dependent and affected by their structures, in which cyanidin-3-glucoside uptake was higher than pelargonidin-3-glucoside. No metabolites from Caco-2 cell activity were detected. An increased uptake with a decrease in pH was observed, which may be linked to the increase in anthocyanins stability and may indicate the role of proton co-transporter. This also suggests that the jejunum would be the favourable section of small intestine for anthocyanin uptake. Reduced anthocyanin uptake in the presence of glucose suggested that facilitative glucose transporter could be involved in the uptake of anthocyanins by Caco-2 cells.