Abstract
Anthocyanins may protect against a myriad of human diseases. However few studies have been conducted to evaluate their bioavailability so their absorption mechanism remains unclear. This study aimed to evaluate the role of two glucose transporters (GLUT1 and GLUT3) in anthocyanins absorption in the human gastric epithelial cells (MKN-28) by using gold nanoparticles to silence these transporters. Anthocyanins were purified from purple fleshed sweet potatoes and grape skin. Silencing of GLUT1 and/or GLUT3 mRNA was performed by adding AuNP@GLUT1 and/or AuNP@GLUT3 to MKN-28 cells. Downregulation of mRNA expression occurred concomitantly with the reduction in protein expression. Malvidin-3-O-glucoside (Mv3glc) transport was reduced in the presence of either AuNP@GLUT1 and AuNP@GLUT3, and when both transporters were blocked simultaneously. Peonidin-3-(6′-hydroxybenzoyl)-sophoroside-5-glucoside (Pn3HBsoph5glc) and Peonidin-3-(6′-hydroxybenzoyl-6″-caffeoyl)-sophoroside-5-glucoside (Pn3HBCsoph5glc) were assayed to verify the effect of the sugar moiety esterification at glucose B in transporter binding. Both pigments were transported with a lower transport efficiency compared to Mv3glc, probably due to steric hindrance of the more complex structures. Interestingly, for Pn3HBCsoph5glc although the only free glucose is at C5 and the inhibitory effect of the nanoparticles was also observed, reinforcing the importance of glucose on the transport regardless of its position or substitution pattern. The results support the involvement of GLUT1 and GLUT3 in the gastric absorption of anthocyanins.
Highlights
Positive correlations have been established between the consumption of flavonoid-rich foods and health benefits, in different in vitro and animal studies, and in several epidemiological studies[1,2]
Preliminary studies with a gastric cell barrier (MKN-28) model indicated that anthocyanins uptake involves a saturable transport but the absorption mechanism remains unknown[6]
In the case of anthocyanidins the hypothesis of transport by passive diffusion can be raised due to their higher hydrophobicity, but this hypothesis is not viable for anthocyanins due to the presence of the glucose moiety. It is highly unlikely for the glucose molecule to cross the cell membrane without a transporter system
Summary
Positive correlations have been established between the consumption of flavonoid-rich foods and health benefits, in different in vitro and animal studies, and in several epidemiological studies[1,2]. Anthocyanins are poorly absorbed as genuine parent glycosides or detected in blood as metabolites[4,5]. The bioavailability of these compounds cannot be addressed only from a simple nutritional perspective. These pigments have unique physical-chemical properties that affect their behavior in vivo. Considering in vivo conditions, anthocyanins are readily metabolized, degraded or excreted from the organism. Due to their rapid appearance in plasma, the absorption of anthocyanins is likely to occur at the gastric level, the information on this topic is scarce[3]. Glucose transporters have been suggested as the main transporters involved in the absorption of these nutraceuticals[7]
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