Effects of Chronic High Sucrose With Dietary or Drinking Inclusion on the Electrogenic Glucose Absorption in the Intestinal Tract of Mice (Mus musculus)
Date
2018-10-16
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Masters
Abstract
The long-term impact of high sugar diets, a factor in the development of obesity and type-2
diabetes, on the intestinal electrogenic sodium dependent glucose transport, the first portal of
entry for glucose, is unknown. Here female C57bl/6 mice fed a normal standard chow diet, and
20% sucrose in the drinking water for 8 months, or 35% sucrose inclusion in the diet for 12
months were assessed. The drinking water sucrose treated mice developed obesity, whereas the
solid dietary sucrose treated mice did not. Jejunal, ileal and colonic segment differences for
electrogenic sodium dependent glucose transport kinetics, mRNA expression of sodium
dependent glucose transporters, inflammatory mediators, and insulin signaling genes were
assessed in all groups, as novel differences between segments were found in normal mice. Ex
vivo intestinal Ussing chamber studies in normal mice characterizing the electrogenic sodium
dependent glucose transport followed Hill Equation sigmoidal kinetics demonstrating low
affinity, high capacity transport (Vmax of 100.8 ± 24.2 uA/cm2, K0.5 17.6 ± 0.9 mM) in the
jejunum, high affinity, high capacity transport in the ileum (Vmax of 111.4 ± 17.5 uA /cm2, K0.5
7.4 ± 1.0 mM) and the absence of transport in the colon. The preferential fit of the kinetics to the
Hill Equation sigmoidal kinetics in each of the tissues, suggest mouse SGLT are working
allosterically, or that there are multiple transporters working together to create the currents
observed, more than in other mammals previously reported. Although segmental differences in
inhibition by dapagliflozin, an SGLT2 inhibitor or phloridzin dihydrate, an SGLT1 inhibitor
were evident, gene expression analysis of the SGLT 1- 6 could not fully explain these regional
differences in kinetics. Non-the-less, the kinetics were highly modified by sucrose treatments,
with a significant shift in the segmental transport, with a decrease in transport in the proximal
segments of the intestine and increase distally in both groups. Most notable was, a significant increase in the Vmax and K0.5 in the ileum of drinking water sucrose treated mice and the
appearance of colonic glucose induced Hill equation kinetic transport in the solid dietary sucrose
treated mice. Interestingly, the novel currents induced in mice treated with both drinking water
sucrose and solid dietary sucrose diet were insensitive to inhibition by dapagliflozin or
phloridzin dihydrate. This indicates that neither SGLT1 or SGLT2 were responsible for the
changes in transport induced by the treatments. Paradoxically, the mRNA expression of SGLT1
was significantly increased in the jejunum, ileum and colon of the drinking water sucrose treated
mice and, SGLT2 was significantly increased in the jejunum and colon of the solid dietary
sucrose treated mice. Additionally, none of the other SGLT family members known for glucose
transport assessed by qRT-PCR could account for the observed kinetic changes. This is
suggestive of an orphan sodium dependent glucose transporter or posttranslational modification
of the identified transporters. Finally, these kinetic changes do not seem to be caused by
inflammation or dysfunctions in the insulin signaling pathway, as the genes for both
inflammatory mediators and insulin signaling were generally unchanged from control mice in
both groups. The exceptions, not consistent in all segments, was a significant increase in TGF-b1
in the drinking water sucrose treated mouse jejunum and ileum, and IRS-2 in the drinking water
sucrose treated mouse jejunum. Identifying these novel segmental kinetic differences in
electrogenic glucose absorption in the mouse intestine and the changes induced by chronical
sucrose provided in the drinking water, including the appearance of a putative orphan
transporter, not only adds to the understanding of the pathophysiology of the obesity, type-2
diabetes but could direct future therapy.
Description
Keywords
glucose transport, intestine, sucrose
Citation
Degree
Master of Science (M.Sc.)
Department
Veterinary Biomedical Sciences
Program
Veterinary Biomedical Sciences