Intestinal Permeability in Human Nonalcoholic Fatty Liver Disease

A Systematic Review and Meta-analysis

Toon J. I. De Munck; Pan Xu; Harm J. A. Verwijs; Ad A. M. Masclee; Daisy Jonkers; Jef Verbeek; Ger H. Koek


Liver International. 2020;40(12):2906-2916. 

In This Article


Reporting of this systematic review and meta-analysis was performed according to the PRISMA guidelines (preferred reporting items for systematic reviews and meta-analyses).[18]

Search Strategy

A systematic literature search was conducted in 2020 (week 38) in both PubMed and Embase. The following keywords, synonyms and MeSH terms were used: non*alcoholic fatty liver disease, Nonalcoholic Fatty Liver Disease, fatty liver disease, NAFL, Fatty Liver, Non-alcoholic Fatty Liver Disease, non*alcoholic steatohepatitis, NASH, nonalcoholic steatohepatitis, liver steatosis, hepatic steatosis, liver steatosis, intestinal barrier, gut barrier, gut permeability, permeability, zonulin. This resulted in 1070 hits and after exclusion of duplicates, 783 were included for screening of abstracts and full text. In addition, references of selected articles were assessed and included if suitable.

Eligibility Criteria

Studies on in vivo IP measurements in human NAFLD patients were included in this systematic review. Studies were eligible for inclusion when the following inclusion criteria were met: (i) original peer reviewed research paper in English, (ii) the study population or a subgroup of the population consist of NAFLD patients (diagnosed with liver biopsy or imaging) without cirrhosis (because cirrhosis itself can lead to an increased IP), (iii) in vivo IP measurements (ie by urinary excretion of orally administered sugars, 51Cr-EDTA or polyethylene glycol or by serum zonulin levels) and (iv) comparison of IP between groups (healthy controls (HC) vs NAFLD or NAFL vs NASH). Exclusion criteria included: (i) review articles, letter to the editor, commentaries, (ii) animal studies, (iii) studies investigating ex vivo permeability (ussing chambers) and solely microbial translocation via endotoxin/lipopolysaccharide (LPS) levels.

Selection Process and Data Extraction

To reduce selection bias, all titles and abstracts were screened for eligibility (based on in- and exclusion criteria) independently by two authors (HV, TDM). After consensus full text of selected articles were again independently checked for eligibility by the same authors (HV, TDM). Furthermore, both authors independently extracted all data using standardized data extraction forms. Data on patient characteristics (HC and NAFLD), method of NAFLD diagnosis (imaging or biopsy), IP test, main outcome (IP comparison between groups and relationship to liver histology) and observed correlations between the degree of IP and clinical factors was extracted. In case of disagreement on eligibility, the two reviewers came to consensus after discussing the article with a third reviewer.

Quality Assessment

The methodological quality of the selected studies was assessed by two independent researchers (HV, TDM) using the Newcastle-Ottawa Quality Assessment Scale (NOS) for case-control studies.[19] The NOS-score was converted to (Agency for Healthcare Research and Quality) AHRQ standards using the following thresholds: good quality: 3 or 4 stars in the 'selection' domain AND 1 or 2 stars in 'comparability domain' AND 2 or 3 stars in 'exposure' domain. Fair quality: 2 stars in the 'selection' domain AND 1 or 2 stars in 'comparability domain' AND 2 or 3 stars in 'exposure' domain. Poor quality: 0 or 1 star in the 'selection' domain OR 0 stars in 'comparability domain' OR 0 or 1 stars in 'exposure' domain.

Statistical Analysis

Meta-analyses were performed using a random effect model with Review Manager version 5.3 if at least two studies evaluated a similar IP marker and compared this marker between HC and NAFLD patients or between biopsy proven NASH and NAFL (NAFLD not NASH) patients. Because of different test characteristics studies investigating small intestinal permeability by means of urinary recover of orally administered sugars (5–6 h L/M or L/R) and by means of serum zonulin, were pooled separately. Because of differences in physicochemical properties, data on 24 h urinary collection of 51Cr-EDTA and sucralose were not pooled. If both a BMI matched (or obese) control group and a normal weight control group were available in one study, data of the BMI matched control group was used in the analysis. All data were entered as mean ± SD. When the original results were only reported as median and (IQR) we estimated mean and SD using the formula proposed by Wan et al.[20] In the studies where the data were included in figures and not provided numerically, we used software program Plot Digitizer to extract data. The pooled standardized median difference with 95% CIs were presented in forest plots. Heterogeneity of study results was tested with χ 2 and I 2 calculations. We intended to assess publication bias by visual examination of the funnel plot and the Egger test for funnel plot asymmetry.