Abstract
This study compared the ability of nine culinary plant extracts containing a wide array of phytochemicals to inhibit fructose uptake and then explored the involvement of intestinal fructose transporters and phytochemicals for selected samples. The chemical signature was characterized by high performance liquid chromatography with mass spectrometry. Inhibition of [14C]-fructose uptake was tested by using human intestinal Caco-2 cells. Then, the relative contribution of the two apical-facing intestinal fructose transporters, GLUT2 and GLUT5, and the signature components for fructose uptake inhibition was confirmed in naive, phloretin-treated and forskolin-treated Caco-2 cells. HPLC/MS analysis of the chemical signature revealed that guava leaf contained quercetin and catechin, and turmeric contained curcumin, bisdemethoxycurcumin and dimethoxycurcumin. Similar inhibition of fructose uptake (by ~50%) was observed with guava leaf and turmeric in Caco-2 cells, but with a higher contribution of GLUT2 for turmeric and that of GLUT5 for guava leaf. The data suggested that, in turmeric, demethoxycurcumin specifically contributed to GLUT2-mediated fructose uptake inhibition, and curcumin did the same to GLUT5-mediated fructose uptake inhibition, but GLUT2 inhibition was more potent. By contrast, in guava leaf, catechin specifically contributed to GLUT5-mediated fructose uptake inhibition, and quercetin affected both GLUT5- and GLUT2-mediated fructose uptake inhibition, resulting in the higher contribution of GLUT5. These results suggest that demethoxycurcumin is an important contributor to GLUT2-mediated fructose uptake inhibition for turmeric extract, and catechin is the same to GLUT5-mediated fructose uptake inhibition for guava leaf extract. Quercetin, curcumin and bisdemethoxycurcumin contributed to both GLUT5- and GLUT2-mediated fructose uptake inhibition, but the contribution to GLUT5 inhibition was higher than the contribution to GLUT2 inhibition.
Highlights
Accumulating evidence indicates that high fructose consumption leads to the development of obesity, diabetes and dyslipidemia in experimental animals
Caco-2 cells, we demonstrated the relative importance of these two intestinal fructose transporters in inhibiting fructose transport by guava leaf and turmeric extracts
The data obtained in this study clearly indicated that different components in each extract have different contributions to fructose transport inhibition by influencing GLUT2 or GLUT5 at the apical side of cells, suggesting a possibility that guava leaf and turmeric extracts might be useful to reduce the risks of obesity, diabetes or dyslipidemia from excessive fructose intake
Summary
Accumulating evidence indicates that high fructose consumption leads to the development of obesity, diabetes and dyslipidemia in experimental animals. Unlike glucose, absorbed fructose is nearly completely metabolized in the liver through the sequential actions of fructokinase, aldolase B and triokinase, which are not inhibited by ADP and citrate [1]. Due to this absence of feedback inhibition, almost all fructose absorbed is converted into hepatic triose-phosphate regardless of the cellular energy status [2]. There is compelling evidence that consumption of fructose with fruits or honey does not yield the same unfavorable effects as added fructose, probably due to the presence of dietary fibers and/or phytochemicals
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