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Advances in Microbiology, 2013, 3, 212-221
doi:10.4236/aim.2013.32032 Published Online June 2013 (http://www.scirp.org/journal/aim)
Clinical Studies Evaluating Effects of Probiotics on
Parameters of Intestinal Barrier Function
Saskia van Hemert1*, Jurre Verwer1, Burkhard Schütz2
1Winclove Probiotics, Amsterdam, the Netherlands
2Biovis Diagnostik MVZ GmbH, Limburg-Offheim, Germany
Email: *Saskiavanhemert@winclove.nl
Received March 6, 2013; revised April 4, 2013; accepted May 4, 2013
Copyright © 2013 Saskia van Hemert et al. This is an open access article distributed under the Creative Commons Attribution Li-
cense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
The intestinal barrier is important in preventing translocation of bacteria, toxins and antigens from the lumen of the gut
into the body. Enhanced permeability, or gut leakiness, has been associated with different diseases. Probiotics can,
strain-specifically, improve the epithelial barrier function. However, so far most researches have used cell lines or ani-
mal models due to the difficulty of measuring the effects of products on the epithelial barrier function in vivo in humans.
Here a systematic literature search was performed to find articles addressing the effects of probiotics on the barrier
function in human trials. The Pubmed database was searched (January 2013) to identify human in vivo studies with pro-
biotic products in which parameters for epithelial barrier function were measured. In total 29 studies were identified, but
patients, bacterial characteristics and methods to measure intestinal barrier function caused large heterogeneity among
these studies. About half of the studies showed positive results of probiotics on the epithelial barrier function, indicating
a clear potential of probiotics in this field. In a case series of 14 patients using Ecologic825, a probiotic food supple-
ment with known effect on epithelial barrier function, different markers of intestinal integrity improved significantly.
Further studies in this field should consider strain(s), dose and duration of the probiotic supplementation as well as the
markers used to measure epithelial barrier function. Besides the lactulose/mannitol test, zonulin and α1-antitrypsin
might be valuable markers to measure epithelial barrier function in future experiments.
Keywords: Bacteria; Epithelial Barrier; Gut Permeability; Intestinal Barrier Function; Intestinal Integrity; Probiotics;
Review; Vivo Studies
1. Introduction
The intestinal epithelial cells have a dual function. On
one hand they facilitate absorbance and transport of nu-
trients, electrolytes and water. On the other hand they
also form a barrier between the body and the bacteria,
toxins and antigens present in the gut. The ability to con-
trol the invasion of harmful content from the lumen to
the body is called the intestinal barrier function. This
defense mechanism consists of multiple elements, like
the mucous layer, secretory IgA, antimicrobial peptides,
and the apical junction complex. The latter is composed
of tight junctions, adherence junctions and desmosomes.
The tight junctions seal the paracellular pathway and are
the rate-limiting step in the transport between adjacent
epithelial cells [1].
The intestinal barrier can be disturbed by various causes,
like certain medicines, exercise, mast cell activation, high
fat diet, stress, etc. [1]. This can lead to an increased per-
meability, allowing amongst others enhanced entrance of
lipopolysaccharides (LPS) into the body. LPS are parts of
the outer membrane of Gram-negative bacteria and are
strong endotoxic compounds. They can cause the release
of pro-inflammatory cytokines in the body, leading to
inflammation. Increased permeability of the epithelial bar-
rier has been associated with many gastrointestinal in-
flammatory disorders, like inflammatory bowel diseases
(IBD, Crohn’s disease and ulcerative colitis), irritable
bowel syndrome (IBS), food allergies and celiac disease
[2]. In addition, increased permeability can also lead to
systemic inflammatory diseases, like allergy, metabolic
syndrome, diabetes, atherosclerosis, chronic fatigue syn-
drome, autism, migraine and rheumatoid arthritis [3].
Probiotics are living microorganisms that have benefi-
cial effects on the health of the host [4]. Strains docu-
mented as probiotic tend to be species of Lactobacillus or
*Corresponding author.
Copyright © 2013 SciRes. AiM
S. van HEMERT ET AL. 213
Bifidobacterium. More and more is known that probiotic
effects are species- and even strain-specific. Certain pro-
biotics have shown to be effective in different gut-related
diseases, like antibiotic-associated diarrhea and necrotiz-
ing enterocolitis in premature infants [5,6]. For some
other diseases, including IBD the effects of probiotics are
promising, but so far results from clinical trials have
been inconsistent [7]. Probiotics have proven strain-de-
pendent capabilities in vitro as well as in vivo to improve
the epithelial barrier function via different mechanisms
[8,9]. Most work has been done in cell culture systems or
in animal models [9-11]. Effects in humans are difficult
to measure in vivo due to the inaccessibility of the intes-
tine. One way to overcome this problem is by oral ad-
ministration of test substances and measurement of uri-
nary excretion. The lactulose/mannitol (L/M) test or a
comparable sugar test is the most used method to meas-
ure intestinal permeability. Lactulose is a disaccharide
which is passively absorbed through the paracellular path-
way via the tight junctions. Mannitol, which is a mono-
saccharide, is transported via the transcellular pathway.
In the case of heightened permeability, more lactulose
passes the barrier and eventually ends up in the urine.
Therefore, a high lactulose/mannitol ratio represents a
high, i.e. pathological, intestinal permeability. Other test
substances that are used, are 51Cr-EDTA or polyetylene
glycols (PEG). The 51Cr-EDTA test has been used to
detect increased intestinal permeability in Crohn’s Dis-
ease, celiac disease, and non-alcoholic fatty liver disease
[12-14]. Urinary excretion of PEG was significantly
higher in patients with alcoholic liver disease and with
acute pancreatitis compared to healthy controls [15,16].
Disadvantages are that all these methods are not very
sensitive, and that they are affected by intestinal transit
and the renal elimination rate [16]. Alternatively, other
biomarkers for intestinal permeability are sometimes meas-
ured, like intestinal fatty acid binding protein (IFABP),
C-reactive protein (CRP), tumor necrosis factor α (TNF-
α), alpha1-antitrypsin, calprotectin, eosinophil cationic
protein (ECP) and zonulin [17,18]. These biomarkers have
been correlated with barrier function, but do not measure
it directly. IFABP is a protein specifically located in the
apical villi of small bowel mucosa that is released into
the systemic circulation in the event of enterocyte death
and is a marker for enterocyte damage and intestinal
ischemia [19,20]. CRP, TNF-α and ECP are general mar-
kers for inflammation, whereas α1-antitrypsin and cal-
protectin are markers for intestinal inflammation. Zonulin is
a relatively novel marker of permeability [3]. It is a phy-
siologic modulator of the intercellular regulation of tight
junction proteins and thereby the paracellular epithelial
intestinal permeability [21-23]. Moreover, the intestinal
permeability can also be assessed by measuring the bac-
terial translocation (BT) through analysis of mesenteric
lymph nodes (MLN) or blood plasma by quantitative or
qualitative PCR.
In this review an overview of human studies is given
in which effects of probiotics on the intestinal barrier
function are investigated. Also a case series with Ecolo-
gic®825 is described, a potential probiotic product which
has shown positive effects on epithelial barrier function
in both a cell culture system (Saskia van Hemert, per-
sonal communication), as well as in a rat model of chronic
water avoidance stress [24].
2. Material and Methods
2.1. Literature Review
The systematic literature search was conducted in Pub-
Med up to 1 January 2013, using the following (truncated)
keywords “probiotic*, lactobacill* or bifidobact* AND
trial AND barrier or permeability”. A second search was
performed with “probiotic*, lactobacill* or bifidobact*
AND epithelial barrier, intestinal integrity or tight junc-
tions”. The search was limited to full-text English written
papers. This resulted in 205 hits. By screening the titles
and abstracts, studies performed in vitro, in animals and
reviews were subsequently excluded. Full text of the re-
maining 25 papers was checked. Additional papers were
found by checking references of pertinent articles and by
searching on “probiotic*” and different methods of meas-
uring intestinal permeability.
2.2. Case Series
In the case series 14 patients, 3 male and 11 female, be-
tween 18 and 65 (mean 46) years of age were included in
September 2011. The participants were informed by their
physician and gave their informed consent to the physi-
cian. All procedures were in accordance with the Hel-
sinki Declaration of 1975. Exclusion criteria were known
inflammatory gastrointestinal diseases, use of probiotics
or antibiotics four weeks prior to the study, use of gastric
acid inhibitors, presence of known diabetes type II and
pregnancy. The patients were supplemented with a daily
dose of >7.5 × 109 cfu Ecologic®825 (Winclove Probiot-
ics) for 8 weeks. Ecologic®825 is a food supplement con-
taining a mixture of 9 bacterial strains: Bifidobacterium
bifidum W23, Bifidobacterium lactis W51, Bifidobacte-
rium lactis W52, Lactobacillus acidophilus W22, Lacto-
bacillus casei W56, Lactobacillus paracasei W20, Lac-
tobacillus plantarum W62, Lactobacillus salivarius W24
and Lactococcus lactis W19. Before the start of the sup-
plementation (t = 0 weeks) and at the end (t = 8 weeks)
blood serum and faeces samples were collected to deter-
mine parameters for impaired barrier function.
2.3. Analyses
Zonulin, α1-antitrypsin and calprotectin in stool samples
Copyright © 2013 SciRes. AiM
S. van HEMERT ET AL.
214
were analyzed with commercially available ELISA kits
(Immundiagnostik AG, Bensheim, Germany) as described
earlier [25]. In the serum levels the following parameters
were measured with standard procedures (Biovis Diag-
nostik): IgG4 antibodies against banana, egg, hazelnut,
cow milk, soy beans and wheat, and high sensitive
(hs)CRP. IgG4 antibodies were measured by DST Ag
Schwerin and the hsCRP on Siemens Immulite 2000. A
lactulose/mannitol test was performed by giving the pa-
tients a mixture of 30 mg mannitol and 150 mg lactulose
stirred into 50 mL non-carbonated mineral water. Urine
samples were analysed by applying the HPLC method of
Immuchrom GmbH Heppenheim.
2.4. Statistics
For the case series, a paired student t-test was used to
measure the significance of the parameters before and
after the intervention period. Differences were consi-
dered significant at 2-tailed p < 0.05.
3. Results and Discussion
3.1. Literature Study
In total 29 studies were found by systemic literature
search, which investigated the effect of a single bacterial
strain or a bacterial mixture on the human intestinal bar-
rier function in vivo (Tables 1 and 2). This was often a
secondary endpoint, as the primary endpoint in most
cases was a decrease in a clinical endpoint. More than
half of the studies (17/31) showed a positive effect of the
used probiotics on epithelial barrier function, whereas the
other studies (13/31) did not show an effect. One study
had two arms and a placebo whereby a positive effect
was found in only one of the arms [26]. In general, the
study groups were small, ranging from 4 to 81 persons
per group. For some studies the small numbers of par-
ticipants might be an explanation for the fact that no sig-
nificant effects were found, for example the study of Al-
berda et al., showed a trend (p = 0.06) with groups of 7
patients only [28]. Most studies (n = 20) had treatment or
alleviation of clinical symptoms as purpose, while a
small group of studies (n = 9) aimed for a preventive
effect [18,28-35]. This effect was sought for example in
preventing bacterial infections in infants, [33] or pre-
venting post-infectious complications [18,30-32,34]. At
first sight, the result consists of a very heterogeneous
assembly of investigations. This variety is reflected in a
number of factors related to the probiotics, to the patient
population and the methodology. The probiotics used in
the studies varied in daily dose, duration of supplementa-
tion and number and type of bacterial strains. The patient
population ranged from healthy volunteers to critically ill
patients and preterm infants. The use of medicines like
non-steroid anti-inflammatory drugs and antibiotics are
an additional factor of variation in the patient population.
There were also marked differences between the power
of the studies, methodological quality of the studies and
the analytical methods to measure intestinal barrier func-
tion. The heterogeneity found in this literature review, is
also found in other recent reviews summarizing for ex-
ample the role of probiotics in the treatment of eczema,
IBD and IBS [36-38]. The heterogeneity caused by the
probiotic regime, the patient population and the method-
ology of measuring epithelial barrier function will be
discussed below.
3.1.1. Probiotic Regime
One of the variables related to the used probiotics is the
daily dose. This ranged from 1 × 109 colony forming
units (CFU) [28] to 1 × 1012 CFU [35] of the studies
yielding positive effects and from 1 × 109 CFU [39] to 9
× 1011 CFU [27] of the studies with no clear benefit on
barrier function. When looking at the mean daily dose,
the positive studies administered on average 1 × 1011
CFU, while the studies without positive effects used 8 ×
1010 CFU, a negligible difference on the log-scale used to
determine the CFU. Also the medians were very similar,
1 × 1010 CFU in both groups. These results imply that a
relatively high dose is not principally necessary to result
in a positive effect nor does it give any guarantee of such.
Moreover, different patient groups might benefit from
different daily doses to elicit effects.
The duration of supplementation in the studies also
varied strongly, from 1 [35] to 183 days [40] in the posi-
tive studies and from 2 [41] to 92 day [42] in the studies
without an effect. The mean durations were 40 vs. 28
days for studies with a positive effect and no effect re-
spectively, whereas the medians were 28 days for both
groups of studies. Some authors suggested that the lack
of a positive outcome was due to a too short intervention
duration [31,43]. However other longer studies did not
find any positive effect as well [42,44]. One interesting
finding is the loss of the beneficial effect over time. In
the study of Gupta et al. [40] a positive effect on intesti-
nal permeability was found after 12 weeks, but this effect
was lost after 24 weeks, despite a supplementation during
24 weeks. Finally, studies were also checked for a fol-
low-up period, to speculate on the persistence of a bene-
ficial effect of probiotics. Only two studies specifically
defined a follow-up test but neither of both tested the
intestinal permeability at that time [45,46]. Although the
clinical symptoms remained lower in the probiotics group,
nothing can be said about the persistent effects on intes-
tinal permeability.
From in vitro studies it is already known that bacterial
strains can vary considerably on their effects on epithe-
lial barrier function [8,47]. Also the studies in this review
Copyright © 2013 SciRes. AiM
S. van HEMERT ET AL.
Copyright © 2013 SciRes. AiM
215
aAT = α1-antitrypsin; BT = bacterial translocation; C = cellobiose; CRP = C-reactive protein; IFABP = intestinal fatty acid binding protein; L = lactulose; LPS = lipopolysacchariden; M = mannitol; PEG = poly eth-
ylene glycol; sCD14 = soluble CD14; TJ = tight junction; bB = Bifidobacterium; E = Enterococcus; L = Lactobacillus; Lc = Lactococcus; Leuc = Leuconostoc; LGG = Lactobacillus rhamnosus GG; P = Propionibac-
terium
;
S = Stre
p
tococcus
;
n.d. = not
d
escribed.
Table 1. Studies with probiotics showing an improvement in epithelial barrier function.
S. van HEMERT ET AL.
216
aAT = α1-antitrypsin; BT = bacterial translocation; C = cellobiose; CRP = C-reactive protein; IFABP = intestinal fatty acid binding protein; L = lactulose; LPS = lipopolysacchariden; M = mannitol; PEG = poly eth-
ylene glycol; sCD14 = soluble CD14; TJ = tight junction; bB = Bifidobacterium; E = Enterococcus; L = Lactobacillus; Lc = Lactococcus; Leuc = Leuconostoc; LGG = Lactobacillus rhamnosus GG; P = Propionibac-
terium; S = Streptococcus.
Table 2. Studies with probiotics not showing an improvement in epithelial barrier function.
Copyright © 2013 SciRes. AiM
S. van HEMERT ET AL.
Copyright © 2013 SciRes. AiM
217
used a variety of strains whereby L. rhamnosus (mainly
LGG) and L. plantarum were the most used species.
Strain selection is an important point in the design of
studies with probiotics as the effects can vary largely
between strains. It has been suggested that multispecies
probiotic products (products with multiple strains, pref-
erentially of different genera) are in general more effec-
tive compared to monospecies products (containing a
single strain) [48,49], but for the studies in this review
the results were comparable for monostrain and multis-
pecies products. Monostrain products were used in 10
studies with a positive outcome and 8 studies without a
beneficial effect on barrier function, whereas multispe-
cies products were involved in 8 studies with a positive
outcome and 7 studies without beneficial effect. How-
ever, for the large majority of the studies it was not de-
scribed how the used strains were selected or why these
specific strains were used.
3.1.2. Patient Groups
Another point of interest is the variation of patient groups
in the studies reviewed. While patients with atopic ec-
zema/dermatitis suffer from inflammatory processes lead-
ing to or even might be caused by barrier dysfunctions in
the skin and gut, the clinical manifestation in acute pan-
creatitis or other critically ill patients is quite different.
Different pathological mechanisms can lead to various
problems with the epithelial barrier, perhaps requesting
diverse probiotic approaches.
3.1.3. Measurement of Intestinal Permeability
Besides heterogeneity in the bacterial strains and the pa-
tient group, the method of measuring the intestinal per-
meability was a third source of heterogeneity. While the
majority of the studies used a sugar absorption test (19
out of 29), the used sugars were variable (lactulose, man-
nitol, cellobiolose, sucrose or rhamnose). Other methods
were PEG and in some studies tight junction protein
staining was used. IFABP or IgA/IgG were additionally
measured in some studies [17,18,50] as indirect indices
of the epithelial barrier integrity. CRP, TNF-α, α1-anti-
trypsin, mesenteric lymph nodes biopsies and PCR were
often used to assess inflammatory and/or bacterial activ-
ity or translocation. Measuring bacterial translocation to
the mesenteric lymph nodes can only be done in studies
with operations. This method does not seem to correlate
with results of a sugar test [51] and it has been suggested
that bacterial translocation after abdominal surgery may
be part or normal antigen-sampling processes of the gut
[18]. The two studies with HIV-infected individuals both
used PCR on blood plasma to determine microbial trans-
location, whereas this method has not been used in any of
the other studies with probiotics. Whereas this method is
relevant to measure intestinal barrier function remains to
be determined, as liver function might also influence the
levels of bacterial DNA in blood plasma. A relatively
novel marker of barrier function is zonulin, which was
used in a recent study with probiotics [25]. Zonulin has
been suggested as one of the most valid surrogate mark-
ers to estimate intestinal barrier function in humans [52].
There is no evidence that one specific method is more
sensitive than another. In studies using the L/M ratio an
effect was not found more often than studies using other
sugar tests. However, in all studies using PEG no effect
was observed [17,18,53]. Interestingly in one study ef-
fects of probiotic supplementation on plasma levels of
LPS were observed, despite a lacking effect as measured
with PEG [53]. Although the L/M test or a comparable
sugar test was often used, this method had some draw-
backs. First, due to the lack of a standardization [54], the
L/M ratio varies considerably even among healthy indi-
viduals. Indeed, the investigators of the current articles
differ in their normal values of the L/M ratio regarding
what is physiological and pathological. Second, the
quantity of sugars used varied from 250 mg to 10 g for
lactulose and from 100 mg to 5 g for mannitol. Although
the absolute quantities used might not be of major influ-
ence, as the eventual ratio is a relative value, the osmo-
larity of the test solution can have influenced the out-
comes [54]. Other methods to measure intestinal perme-
ability are 51Cr-EDTA and 99mTcDTPA, which are non-
degraded radio-labeled chelates used to measure intesti-
nal permeability [55], but so far they have not been used
by studies with probiotics.
3.2. Case Series
To investigate which parameters are useful to measure in
relation to probiotics and epithelial barrier function, we
measured different parameters related to barrier function
in a case series of 14 patients.
Zonulin levels in faeces were elevated (>30 ng/ml) in
10 of the 14 people participating in the case series before
the start of the intervention. The average zonulin levels
decreased significantly after the 8 weeks intervention
period (p < 0.01, Figure 1(a)). In the group of people
started with elevated zonulin levels, the levels decreased
in 8 of the 10 persons during the intervention period. In
the control group 2 of the 4 persons showed decreased
zonulin levels after 8 weeks of intervention. Alpha1-
antitrypsin levels were elevated in 7 out of the 14 people
before the start of the intervention period (>27.2 mg/dl)
and it decreased significantly after the intervention (p <
0.01, Figure 1(b)). These levels were decreased in 6 of
the 7 people starting with elevated levels, and also in 6 of
the 7 people starting with levels in the normal range
(<27.2 mg/dl). Interestingly the person who started with
elevated levels of alpha1-antitrypsin, but didn’t show a
S. van HEMERT ET AL.
218
Figure 1. Effect of 8 weeks supplementation with Ecologic825 on the average levels of (a) zonulin; (b) α1-antitrypsin and (c)
hsCRP. Normal values are indicated with a dotted line. The average values are indicated in bold .
decrease also did not show a decrease in zonulin. The
three persons who had the highest zonulin levels before
the start of the study also had the highest alpha1-anti-
trypsin at the start. High sensitive CRP was measured in
only 9 people, due to technical problems. The levels were
elevated in 5 of the 9 people before the start of the trial
(>0.55 mg/l). Those levels were decreased in all five par-
ticipants which had elevated levels before the start of the
intervention, but not in the persons which started with
normal values (Figure 1(c)). The IgG4 antibodies against
food allergens (measured in 9 of the 14 people) did not
show any differences before and after the intervention
(results not shown). Calprotectin levels were in all cases
under the detection limit of 10 mg/l. In addition there
were also no differences found with the L/M test.
The participants in these case series visited their phy-
sician due to gastrointestinal complaints. In our study
elevated levels of three markers of intestinal permeability
were found in the majority of the participants. These
markers were zonulin, α1-antitrypsin and CRP. In this
cases series, zonulin levels were measured in faeces, as
was also done in a study investigating the effects of pro-
biotic supplementation in trained men [24]. Measure-
ments of zonulin have also been performed is intestinal
tissue and serum. Tissue levels of zonulin in the intestine
were much higher in celiac patients compared to controls
[21]. Higher levels of zonulin in serum correlate with
higher intestinal permeability as measured with the L/M
test [56,57]. This is in contrast with our study, where no
abnormal L/M ratio was measured while we did find
changes in zonulin levels. This might indicate that zonu-
lin is a more sensitive marker of intestinal barrier func-
tion than the L/M test.
Alpha1-antitrypsin is a marker used as a measure of
protein leakage into the intestinal tract and for inflamma-
tion in individuals with IBD [58]. In the case series a
significant decrease in the levels of α1-antitrypsin in fae-
ces was detected. A similar decrease of levels of α1-an-
titrypsin was found in a study with probiotics in children
with cow-milk allergy [26], but not in a study with pro-
biotics in trained men [25]. This latter finding might be
due to the fact that the α1-antitrypsin levels were not
elevated before the start of the study in the study popula-
tion, whereas this was the case in the described case se-
ries and the study of Viljanen et al. [26]. As inflamma-
tion is linked to impaired intestinal barrier function [59]
it is not surprising that a marker for inflammation might
also be valuable as a marker for barrier function. Faecal
calprotectin is, similar as α1-antitrypsin, used as marker
in IBD [60], but the levels of calprotectin were below the
detection limit of 10 mg/L in the studied patient group.
This might indicate that in contrast to α1-antitrypsin,
calprotectin is not a useful marker for subtle intestinal
barrier problems, but more relevant in diseases like IBD
with marked inflammation of the epithelial barrier func-
tion. Another marker for inflammation is CRP, which
was also identified in the case series. In another study
CRP tended to be higher in obese patients compared with
healthy weight controls [61]. CRP levels were associated
with certain faecal metabolites and were inversely corre-
lated with the total microbial counts, indicating a possi-
ble influence of the gut microbiota on CRP levels. Ele-
vated CRP levels were correlated with enhanced L/M
ratios in some studies [62,63], but not in all [64]. This
suggests that increased levels might be caused by en-
hanced intestinal permeability, but can also have other
causes. These elevated levels of CRP might indicate a
systemic response to increased LPS in the body due to an
enhanced permeability of the gut. From that perspective,
CRP is not a direct measurement of intestinal permeabil-
ity, but is probably more an indirect measurement.
3.3. Wider Implications
The primary aim of this narrative review was to provide
Copyright © 2013 SciRes. AiM
S. van HEMERT ET AL. 219
an intensive overview of the current literature regarding
the influence of probiotics on the human intestinal barrier
function. This review is, to our knowledge, the first to
overview the literature of probiotics and intestinal per-
meability in in vivo human studies. Overall, there are
several indications in vivo that probiotics can have posi-
tive effects on the barrier function, as a positive effect
was found in 48% of the controlled studies. The hetero-
geneity of the studies makes it impossible to draw any
conclusions on probiotic treatment specifications. It is
plausible that different patient groups might benefit from
different treatment plans, such as daily dose, strain and
duration. Moreover, different disturbances of the gut bar-
rier might also ask for different barrier measurements.
The case series indicated that zonulin, α1-antitrypsin and
hsCRP might be valuable markers to measure intestinal
permeability in vivo. Clearly, more investigations have to
be conducted to draw strong conclusions. For these in-
vestigations consensus is necessary on standardized meth-
ods to measure barrier function.
4. Acknowledgements
The authors like to thank the participants of the case se-
ries for their participation in the study.
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