Dietary and developmental regulation of intestinal sugar transport

Abstract

The Na+-dependent glucose transporter SGLT1 and the facilitated fructose transporter GLUT5 absorb sugars from the intestinal lumen across the brush-border membrane into the cells. The activity of these transport systems is known to be regulated primarily by diet and development. The cloning of these transporters has led to a surge of studies on cellular mechanisms regulating intestinal sugar transport. However, the small intestine can be a difficult organ to study, because its cells are continuously differentiating along the villus, and because the function of absorptive cells depends on both their state of maturity and their location along the villus axis. In this review, I describe the typical patterns of regulation of transport activity by dietary carbohydrate, Na+ and fibre, how these patterns are influenced by circadian rhythms, and how they vary in different species and during development. I then describe the molecular mechanisms underlying these regulatory patterns. The expression of these transporters is tightly linked to the villus architecture; hence, I also review the regulatory processes occurring along the crypt-villus axis. Regulation of glucose transport by diet may involve increased transcription of SGLT1 mainly in crypt cells. As cells migrate to the villus, the mRNA is degraded, and transporter proteins are then inserted into the membrane, leading to increases in glucose transport about a day after an increase in carbohydrate levels. In the SGLT1 model, transport activity in villus cells cannot be modulated by diet. In contrast, GLUT5 regulation by the diet seems to involve de novo synthesis of GLUT5 mRNA synthesis and protein in cells lining the villus, leading to increases in fructose transport a few hours after consumption of diets containing fructose. In the GLUT5 model, transport activity can be reprogrammed in mature enterocytes lining the villus column. Innovative experimental approaches are needed to increase our understanding of sugar transport regulation in the small intestine. I close by suggesting specific areas of research that may yield important information about this interesting, but difficult, topic.

Acute effects of ingesting glucose solutions on blood and plasma volume

“…It is well known that the activity of the intestinal sodium -glucose co-transporter is strongly influenced by the carbohydrate content of the diet (22) , and it seems likely that variations in the composition of the diet will account for part of the large inter-individual variability that is seen in the rates of gastric emptying and intestinal absorption. Although the transporter is upregulated in animals when carbohydrate is added to the diet, the response seems to be too slow to have any acute effect on the time scale of the present study, especially as the amount of glucose administered in the present study is small relative to the normal daily intake.…”

Intestinal fructose transport and malabsorption in humans

“…Mammals receive nutrition prior to weaning from milk, which contains the sugars glucose and galactose, which are transported by SGLT1 and GLUT2. Mammals do not appear to transport fructose until such time as it would naturally arise in their diet (7), and the expression of GLUT5 has been shown to be developmentally regulated (17,21). The capacity for fructose uptake in neonatal rats was paralleled by GLUT5 expression, with GLUT5 expressed at a low level through the suckling (0 -14 days of age) and weaning (14 -28 days) stages, but increasing dramatically after 28 days (57).…”

Verfügbarkeit phenolischer Komponenten aus Rotwein (Lemberger) und Rotem Traubensaft für den Menschen

“…Als Versuchspersonen dienten 9 gesunde Probanden (4 ♂, 5 ♀) im Alter von 24-34 Jahren und einem BMIbereich von [20][21][22][23][24][25][26] [2-4, 8, 9, 11-15]. Die im allgemeinen niedrigen Plasma-und Urinkonzentationen lassen vermuten, dass die in geringem Mass resorbierten Anthozyandosen einem raschen Metabolismus unterworfen sind, wobei auch ein Abbau bis hin zur Protokatechusäure im Plasma von Ratten nachgewiesen werden konnte nach Verfütterung einer allerdings 100 -fach höheren Dosis pro kg KG als in der vorliegenden Studie [10].…”

“…Ebenso scheinen nach jüngeren Daten die intestinale Laktase-Phlorizin-Hydrolase (LPH) in der apikalen Membran intestinaler Epithelzellen und die zytosolische β-Glukosidase bei Resorption und Metabolismus von Flavonoiden eine nicht unwichtige Rolle zu spielen [19,20]. Unter Berücksichtigung des Zuckergehalts des getesteten Traubensafts und der Strukturähnlichkeit zu Querzetin andererseits ist es denkbar, dass die Anthozyane via Kotransport mit dem intestinalen, membrangebundenen SGLT-1 resorbiert wurden mit dem Ergebnis einer erhöhten Aufnahme aus dem Intestinaltrakt gegenüber dem verwendeten Rotwein [21].…”