The effects of differential SCFA availability on human substrate and energy metabolism

Gut microbiota is being increasingly recognized as an important factor in fat
distribution, insulin sensitivity and glucose and lipid metabolism.
Accordingly, the intestinal microbiota could play an important role in the
development of obesity and type 2 diabetes mellitus. The role of gut-derived
short-chain fatty acids (SCFA), the formation of which is enhanced by microbial
fermentation of fibre, is still controversial. One study found that an increase
in the formation of SCFA stimulated energy extraction from diet, with
subsequent weight gain. In contrast, supplementation of non-fermentable
carbohydrates, which lead to an increase in SCFA formation, had beneficial
effects on body weight control and insulin sensitivity. Of note, a study showed
that butyrate supplementation in mice prevented diet-induced obesity and
insulin resistance. At the present time, our understanding of the effects of
SCFA on human metabolism (in gut or systemically) is still limited. Yet, in
light of the health claims of certain dietary fibres (prebiotics), a detailed
picture of the physiology of human SCFA metabolism and its interaction with the
microbiome is of pivotal importance. We hypothesize that the differential
availability of SCFA impacts human metabolism differently. To determine whether
rectal administration of SCFA is a good model for studying the metabolic
effects of SCFA we first perform this pilot study. In this pilot study we will
determine if rectal administration of sodium acetate has the same effects on
substrate and energy metabolism compared to proximal administration.
The total TIFN project will provide more insight into how increased
availability of a beneficial SCFA mixture might serve as a basis for rational
nutritional strategies in the prevention and treatment of obesity and type 2
diabetes mellitus.

Based on our hypothesis that differential availability of SCFA will have
beneficial effects on substrate and energy metabolism, the following objectives
will be addressed:
In this pilot study we will validate whether rectal administration of SCFA is a
good model for studying the acute metabolic effects of SCFA. For this, it will
be investigated if site of administration (in distal or proximal colon) of
sodium acetate differentially affects parameters of substrate and energy
metabolism and to test the duration of short-term effects of sodium acetate
administration on markers of substrate and energy metabolism.
When the model of rectal administration is a good model for studying sodium
acetate metabolism, this will be applied later on in a short-term and long-term
study. If not, we may have to use a model of proximal infusion in further
studies.

After the screening visit, the subjects will come to the university 8 times in
15 days. During the first 4 days, the subjects will recieve an endoscopic
procedure (sigmoidoscopy or colonoscopy, randomized) at which a catheter is
clipped inside the colon distal or proximal to the flexura hepatica. The
catheter is placed at the first day and will be in place for the next 3 days.
After placement of the catheter, subjects will stay at the university and come
to the laboratory 24, 48 and 72h after initial placement, for the test days.
During the test days (each approximately 6h per test day), colonic infusions of
sodium acetate 100mM, sodium acetate 180mM and placebo (0.9% saline infusion)
in a randomised order will take place. Via a 'ventilated hood' and blood
sampling (10mL each sample) markers of substrate and energy metabolism will be
examined. After the three test days, the catheter will be pulled out and a
wash-out period of a week will follow. After the wash-out period, the subjects
undergo a second endoscopic procedure (sigmoidoscopy or colonoscopy, depending
on the first procedure), at which a catheter is clipped in the colon. After the
endoscopic procedure, the subjects go home with the catheter in situ and come
to the university at 24, 48 and 72h after initial placement of the catheter for
the test days. During the test days, 100mM of sodium acetate, 180mM sodium
acetate or placebo (0.9% saline) will be administered in a randomised order.
Via a 'ventilated hood' and blood sampling from a distal arm vene, markers of
substrate and energy metabolism will be monitored.

Pilot study: All subjects will be studied 2 times, with once infusions in the
proximal colon and once infusions in the distal colon in randomized order, each
with three different infusions in randomized order consisting of:
1. Sodium acetate 100mM (0.984g sodium acetate dissolved in 120 ml water,
isotonic)
2. Sodium acetate 180mM (1.772g sodium acetate dissolved in 120ml water,
isotonic)
3. Placebo (0.9% NaCl in 120ml water)

Study 1: All Subjects will be studied 6 times with different combinations of
SCFA and placebo enemas in randomized order (place of administration depending
on outcome of pilot study).

Study 2: All subjects will be studied 3 times with the most promising SCFA or
SCFA combinations and once a placebo enema in randomized order after 14 days of
intervention.

Subjects will obtain during the screening visit general information about their
health status. In the future there can be general health benefits for the
public, but the volunteers will have no personal benefits by participating in
the study. They will, however, receive a financial contribution for
participating in this study.
There are different burdens volunteers can experience during the study. Burdens
that volunteers can experience are the time spend with the study (subjects will
have to invest approximately 144 hours in the study) and the dietary and
healthy regimen they have to follow. They have to follow the diet exactly as
prescribed and cannot use alcohol during the test days. They also need to
laxate the colon before coming for the endoscopic procedures, which can cause
abdominal cramps and frequent toilet usage. The catheter, which will stay
inside the colon for three days in row, can cause interference with the normal
daily structure of the volunteer. There will be a small part of the catheter
hanging out of the rectum for infusion of the solutions; this can cause
disturbances in daily life.
At this pilot study, blood will be collected via a venous catheter.
Venepunctures can occasionally cause a local hematoma or bruise to occur. Some
participants report pain during venepuncture. In addition, volunteers undergo a
colonoscopy and sigmoidoscopy, which can lead to several complications and has
several risks (complication rate: 2 in 1000 colonoscopies). In patients
undergoing sigmoidoscopies and colonoscopies for medical reasons, there is a
small (0.08%) risk of bowel perforation and bleeding at the biopsy sites. This
risk is expected to be much smaller in the present study, because no severely
ill subjects will be recruited. Complications mainly appear after removal of
polyps. A report of the *gezondheidsraad* mentions a risk of 0.0025% risk of
perforation after screening for cancer in healthy subjects. Some participants
report pain or unpleasant feelings during the endoscopy. Patients will be
sedated with Midazolam (5mg/mL), 2 - 2.5mg during the colonoscopy, but not
during the sigmoidoscopy. Sedative agents can cause respiratory depression,
hypoxia and hemodynamic effects. The risk of these complications is relatively
small and patient*s saturation, heart rate and respiratory rate will be
monitored during the procedure. In the gastroenterology department there is a
lot of experience with these procedures and they are also used in daily
clinical practice. During the proximal placement of the catheter, intermittent
fluoroscopy will be used to ascertain that the catheter is still positioned
correctly. The radiation exposure during the retraction of the endoscope is
minimal (0.06 mSv), which equals less then 10% of normal annual background
radiation.