Intestinal permeability, gut-bacterial dysbiosis, and behavioral markers of alcohol-dependence severity

Abstract

Alcohol dependence has traditionally been considered a brain disorder. Alteration in the composition of the gut microbiota has recently been shown to be present in psychiatric disorders, which suggests the possibility of gut-to-brain interactions in the development of alcohol dependence. The aim of the present study was to explore whether changes in gut permeability are linked to gut-microbiota composition and activity in alcohol-dependent subjects. We also investigated whether gut dysfunction is associated with the psychological symptoms of alcohol dependence. Finally, we tested the reversibility of the biological and behavioral parameters after a short-term detoxification program. We found that some, but not all, alcohol-dependent subjects developed gut leakiness, which was associated with higher scores of depression, anxiety, and alcohol craving after 3 wk of abstinence, which may be important psychological factors of relapse. Moreover, subjects with increased gut permeability also had altered composition and activity of the gut microbiota. These results suggest the existence of a gut-brain axis in alcohol dependence, which implicates the gut microbiota as an actor in the gut barrier and in behavioral disorders. Thus, the gut microbiota seems to be a previously unidentified target in the management of alcohol dependence.

Keywords: alcohol dependence; behavior; gut microbiota; gut permeability; gut–brain axis.

Fig. 1.

Intestinal permeability was measured by using the ⁵¹Cr-EDTA method. (A) Results revealed that, at T1, 26 of 60 patients had elevated gut permeability whereas the remaining 34 patients had normal gut permeability compared with control subjects. Subjects were therefore split into two groups: AD patients with “high” IP and AD patients with “low” IP. (B) A 3-wk alcohol withdrawal induced a total recovery of gut permeability in AD subjects with high IP. Subjects that relapsed during the detoxification program were excluded from analysis, and results were obtained in 43 subjects. AD, alcohol-dependent subjects; CT, control subjects; IP, intestinal permeability. T1 and T2 refer to the beginning and end of alcohol withdrawal, respectively. ***P < 0.001, ^###P < 0.001.

Fig. 2.

Increased intestinal permeability of AD subjects was associated with the persistence of psychological symptoms at the end of alcohol withdrawal. (A) Scores of psychological factors in CT and AD subjects at the beginning (T1) and end (T2) of withdrawal showing that AD subjects with high IP had higher score of depression, anxiety, and alcohol craving at T2. *P < 0.05 vs. CT; **P < 0.01 vs. CT; ***P < 0.001 vs. CT; ^$P < 0.05. (B) Associations of IP measured at T1 with psychological factors assessed at T2. Values are Pearson’s moment correlation coefficients. AD subjects with high IP and low IP are depicted in red and green, respectively. AD, alcohol-dependent; CT, control; IP, intestinal permeability.

Fig. 3.

Gut-microbiota profiles of AD subjects with high and low intestinal permeability at the beginning of alcohol withdrawal. (A) Gut-bacterial profiles were calculated for each subject using the abundance of the bacterial families from 454 pyrosequencing data. Bacterial taxa for which the sum of sequences in all of the samples was less than 0.01% of the total number of sequences were removed from the analysis. Hellinger transformation was applied to the resulting matrix. Subjects were plotted in the map by using nonmetric multidimensional scaling. (B) Relative abundance of bacterial families and genera at the beginning of withdrawal. No significant differences were observed between AD subjects with low IP and controls. Differences observed between AD subjects with high IP and the other two groups are depicted. Results of relative abundance obtained from pyrosequencing are expressed in the percentage of sequences/taxon. *P < 0.05 vs. CT, **P < 0.01 vs. CT, ***P < 0.001 vs. CT, ^$P < 0.05 vs. ADT1 low IP, ^$$P < 0.01 vs. ADT1 low IP. (C) Total bacteria, F. prausnitzii, Bifidobacterium spp., and Lactobacillus spp. were quantified by qPCR in CT and AD subjects at the onset (T1) of alcohol withdrawal. *P < 0.05, ^$P < 0.05, ^$$P < 0.01, ***P < 0.001, ^$$$P < 0.001. (D) Chart depicting the correlations between IP and gut bacteria detected by pyrosequencing and qPCR methods at the beginning of detoxification. Asterisk indicates significant correlations (P < 0.05) and # indicates 0.1 < P < 0.05. (E) Correlations between IP at T1 and gut bacteria measured by qPCR. r indicates Pearson’s coefficient. AD subjects with high IP and low IP are depicted in red and green, respectively. AD, alcohol dependent; CT, control; IP, intestinal permeability; RA, relative abundance. T1 refers to the beginning of alcohol withdrawal.

Fig. 4.

Effect of alcohol withdrawal on gut-microbiota composition. (A) A significant increase in Ruminococcaceae was observed from T1 to T2 in AD subjects with high IP (*P < 0.05). The genera Ruminococcus and Subdoligranulum also increased during withdrawal in AD subjects with high IP but not significantly (^#P = 0.11). The family Erysipelotrichaceae and the genus Holdemania decreased significantly during withdrawal (*P < 0.05) in all subjects. Results of relative abundance obtained from pyrosequencing are expressed in the percentage of sequences/taxon. (B) Abundance of total bacteria, F. prausnitzii, Bifidobacterium spp., and Lactobacillus spp. after 3 wk of alcohol abstinence as measured by qPCR. *P < 0.05 in AD high IP from T1 to T2. AD high IP and low IP are depicted in red and green, respectively. AD, alcohol dependent; CT, control; IP, intestinal permeability. T1 and T2 refer to the beginning and end of alcohol withdrawal, respectively.

Fig. 5.

Metabolomic profiling of AD subjects with high and low IP. (A) Score plots showing clustering of the metabolite profiles analyzed with partial least squares-discriminant analysis. (B and C) Volatile organic compounds belonging to the chemical classes (B) phenols and (C) indoles. *P < 0.05 compared with CT, ***P < 0.001 compared with CT, ^$P < 0.05 AD high IP vs. AD low IP at the same study time, ^$$P < 0.01 AD high IP vs. AD low IP at the same study time, ^#P < 0.05 compared with ADT1 high IP. AD subjects with high IP and low IP are depicted in red and green, respectively. CT subjects are depicted in blue. AD, alcohol-dependent subjects; CT, control subjects; IP, intestinal permeability; RI, relative indices. T1 and T2 refer to the beginning and end of alcohol withdrawal, respectively.

Fig. 6.

Model representing the relationship among alcohol consumption, gut dysfunction, and affective symptoms in the two subsets of alcohol-dependent subjects at both times of alcohol withdrawal. At the beginning of withdrawal (T1), a subset of AD subjects developed affective symptoms that were likely induced by ethanol and that were not associated with gut disorders. In the other subset of AD subjects, alcohol consumption was associated with gut leakiness, gut-microbiota alterations, and affective symptoms. After 3 wk of abstinence (T2), affective symptoms recovered completely in the subset of AD subjects that did not present with gut dysfunction at T1. In the other subset of AD subjects, the gut barrier was restored upon abstinence, but gut dysbiosis was still present at T2 and might be responsible for the persistence of affective symptoms. From these observations, we hypothesize that gut-microbiota alterations could be associated with a more severe form of alcohol dependence and a higher probability of relapse through negative reinforcement mechanisms linked to higher levels of depression, anxiety, and alcohol craving.