Metagenomic Analyses of Alcohol Induced Pathogenic Alterations in the Intestinal Microbiome and the Effect of Lactobacillus rhamnosus GG Treatment

Abstract

Enteric dysbiosis plays an essential role in the pathogenesis of alcoholic liver disease (ALD). Detailed characterization of the alterations in the gut microbiome is needed for understanding their pathogenic role in ALD and developing effective therapeutic approaches using probiotic supplementation. Mice were fed liquid Lieber-DeCarli diet without or with alcohol (5% v/v) for 6 weeks. A subset of mice were administered the probiotic Lactobacillus rhamnosus GG (LGG) from 6 to 8 weeks. Indicators of intestinal permeability, hepatic steatosis, inflammation and injury were evaluated. Metagenomic analysis of the gut microbiome was performed by analyzing the fecal DNA by amplification of the V3–V5 regions of the 16S rRNA gene and large-scale parallel pyrosequencing on the 454 FLX Titanium platform. Chronic ethanol feeding caused a decline in the abundance of both Bacteriodetes and Firmicutes phyla, with a proportional increase in the gram negative Proteobacteria and gram positive Actinobacteria phyla; the bacterial genera that showed the biggest expansion were the gram negative alkaline tolerant Alcaligenes and gram positive Corynebacterium. Commensurate with the qualitative and quantitative alterations in the microbiome, ethanol caused an increase in plasma endotoxin, fecal pH, hepatic inflammation and injury. Notably, the ethanol-induced pathogenic changes in the microbiome and the liver were prevented by LGG supplementation. Overall, significant alterations in the gut microbiome over time occur in response to chronic alcohol exposure and correspond to increases in intestinal barrier dysfunction and development of ALD. Moreover, the altered bacterial communities of the gut may serve as significant therapeutic target for the prevention/treatment of chronic alcohol intake induced intestinal barrier dysfunction and liver disease.

Pathogenesis of alcoholic liver disease: Role of oxidative metabolism

“…In alcohol-treated mice, the PPARγ agonists, rosiglitazone and pioglitazone, increase circulating levels of adiponectin and expression of its receptors in the liver that is associated with SIRT1-AMPK signaling activation. This pathway correlates with the enhanced expression of fatty acid oxidation enzymes and reduction of alcohol-induced steatosis [207][208][209][210][211][212][213] . In addition, PPARγ agonists have anti-inflammatory effects that reduce cytokine expression such as TNF-α, IL-6 and MCP-1 in alcohol-fed mice [207] .…”

“…These protective effects are correlated with the prevention of alcohol-induced oxidative stress, suppression of CYP2E1 expression, inactivation of TLR4, and inhibition of p38 MAPK phosphorylation, which leads to a significant decrease in NF-κB activation and TNF-α production [209] . Results from a placebocontrolled trial have recently shown that the nonabsorbable antibiotic rifaximin modifies the gut microbiota, and protects alcoholic patients from hepatic encephalopathy [210,211] . Similar results have been seen with TLR4 antagonists, which have been recently studied as therapeutic agents for chronic liver diseases, including ALD [212] .…”

Emerging Aspects of Food and Nutrition on Gut Microbiota

“…270 Similarly, chronic ethanol feeding for 8 weeks increased fecal pH and decreased abundance of both Bacteriodetes and Firmicutes phyla with a remarkable expansion of Proteobacteria and Actinobacteria phyla in mice. 229 In a human trial, chronic alcohol consumption resulted in the alteration of the mucosa-associated colonic bacterial composition in a subset of alcoholics, with lower median abundances of Bacteroides and higher Proteobacteria. Furthermore, measurement of serum endotoxin suggests a change in microbial function, rather than abundance, which may lead to increased levels of gut-derived pro-inflammatory factors in chronic alcohol consumption.…”

Role of phosphodiesterase-4 in alcohol-induced organ injury.

“…Alcohol induced alterations in the gut microbiota (dysbiosis) can cause increased intestinal endotoxin production, as well as compromised gut barrier function, leading to increased intestinal permeability and translocation of bacteria and bacterial products [174][175][176][177][178][179]. The frequency of systemic endotoxemia has been observed to be significantly greater in patients with alcoholic cirrhosis than in non-alcoholic cirrhotic subjects [180,181].…”

“…Recently, in a mouse model we have performed metagenomic analyses to examine the effects of chronic alcohol feeding on the gut bacterial microbiome by employing deep 16s rRNA gene sequencing using DNA isolated from fecal samples [179]. The findings from this study showed that alcohol feeding leads to significant shifts in the gut bacterial community with a marked increase in the phylum Proteobacteria which is comprised of gram negative bacteria that contain lipopolysaccharide (LPS/endotoxin) in their cell wall and are the principal source of intestinal endotoxin and systemic endotoxemia.…”