Luminal Fructose Kinetics

Metabolic dysfunction associated steatotic liver disease (MASLD) has been on
the rise worldwide, with a prevalence of approximately 30% . It is the number
one cause of liver transplantation and patients with MASLD have an increased
risk of death by cardiovascular diseases . Major contributing factors include
obesity, insulin resistance and diabetes mellitus type 2 (T2DM). In recent
years, the role of the gut microbiome in the development of MASLD has become
increasingly evident.

Studies have revealed that lactic acid and streptococci bacterial strains in
the (small) intestine are responsible for significant ethanol production, and
our research has further demonstrated a correlation between endogenous ethanol
production and the presence of fatty liver disease. Additionally, it was shown
that oral proton pump inhibitor use was associated with elevated ethanol
levels. From in vitro experiments we know that fructose serves as a substrate
for lactic acid bacteria . Over the past few years, there has been a
substantial increase in dietary fructose consumption, contributing to the
incidence of obesity and related conditions, including MASLD. Fructose,derived
from fruits and honey, is also a prominent component of commonly used
sweeteners such as sucrose and high-fructose corn syrup, commonly found in soda
beverages. This widespread use results in a substantial fructose intake
worldwide. Conventionally fructose is catabolized in the liver through
fructose-1 phosphate pathway, and a recent study in mice showed that in low
dose, approximately90% of the fructose is metabolised in the small intestine
primarily into glucose. However, in higher doses this small-intestinal fructose
clearance capacity was saturated leading to unmetabolized fructose to spill
over in both the colon and liver. Furthermore, this saturation can also lead to
a longer residence time of fructose in the small intestine, which could affect
the small intestine microbial fructose mixed acid fermentation. This can
subsequently drive production of toxic metabolites, such as ethanol, which may
contribute to the accumulation of hepatic fat following fructose consumption.

In this regard, intestinal gluconeogenesis (IGN) appears to be a protective
mechanism as it converts dietary fructose into glucose thereby preventing
fructose fermentation by microbes. However it remains unclear whereas this
process can also occur in the human (small) intestine following fructose
intake. This as most of our understanding of the (small) intestinal lumen comes
from in vitro experiments or measuring final products in feces or peripheral
blood samples, since there are difficulties to access the (small) intestinal
lumen. However, these in vitro samples do not translate to human (small)
intestinal metabolism since they only represent the net result of metabolites
production, excretion, absorption and hepatic passage, underestimating the
actual contribution of (small) intestine.
In this study we therefore aim to elucidate (small) intestinal microbial and
host fructose catabolism by the use of 13C tracking techniques and directly
sampling of the intestinal lumen in healthy and MAFLD/MASH subjects.
Furthermore, we will test if postprandial fructose and ethanol kinetics depend
on the intestinal pH by administration oral PPIs to the participants.

To elucidate host/microbial intestinal (postprandial) fructose kinetics (by
13C incorporation in glucose and ethanol as well as other metabolites) in small
intestinal fluid as well as plasma, urine and breath samples (whole body
metabolism) and establish the role of (small) intestinal luminal pH (which is
increased upon proton pump inhibitor for 4 weeks of oral omeprazole 2dd 40mg)
in biopsy proven MASLD/MASH subjects versus healthy (BMI<25) subjects (n=11
per group).

This study is designed as a non-blinded single center intervention study in
eleven healthy subjects and eleven MASLD/MASH patients performed in the
Amsterdam UMC.

Omeprazole orally given twice a day 40mg for four weeks

Omeprazole
omeprazol has been prescribed for more than twenty years. It is a relatively
safe drug with a small risk of severe side effects. It prevents patients from
getting gastric and duodenal ulcer or irritation of the stomach by gastric
acid. Frequent reported side effects are gastro-intestinal complaints (i.e.
nausea, vomiting, diarrhoea, constipation, stomach pain) and headache.
Sometimes patients experience itch, rash, urticarial, malaise, insomnia and
dizziness and very rare side effects that have been reported are allergic
reactions, thrombocytopenia and leukopenia, muscle weakness, liver failure and
hypomagnesaemia. However since patients only take the omeprazole for four weeks
we don*t expect any side effects.

Nasal-intestinal catheter and gastroduodenoscopy
Gastroscopy will be performed by a gastroenterologist. Gastroduodenoscopy is a
procedure associated with discomfort, but when participants are well fasted it
is very safe. There is always a small risk of complications. For example
bleeding. But this is less than 1% and often because participants use blood
thinners. We won*t include patients who use blood thinners. Positioning of the
nasal intestinal catheter will be done during the gastroscopy.Participants may
experience nausea or throwing up, but this feeling will fade after the catheter
is placed.

Fomepizol
Fomepizol will be administered intravenously. Fomepizol blocks the ADH enzyme
in the liver thereby preventing ethanol metabolism. We expect that ethanol
concentrations will be higher especially in the MASLD group, but it is highly
unlikely that these concentrations reach toxic values. Nontheless there will be
a physican present during administration.

Blood samples
Participants will receive a catheter in a distal vein which enables multiple
blood withdrawals. Of course they still have the discomfort of the placement
but this will be only once per visit. Complications could be a bruise or a sore
spot after placement. Risk of major complications is very small.

X-ray
After placement of the nasal-intestinal catheter we wille take a x-ray to check
the position of the catheter. In total we will take two x-rays to determine and
check the position of the catheter. Radiation exposure is 0.7 mSv per x-ray.