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Figure 1. Worldwide prevalence of cirrhosis secondary to alcohol abuse compared with other cirrhosis etiologies. Modified from Méndez-
[9]
Sánchez et al. . HCV: hepatitis C virus; ALD: alcoholic liver disease; NASH: non-alcoholic steatohepatitis; HBV: hepatitis B virus; NAFLD:
non-alcoholic fatty liver disease
[11]
ADH and then from acetaldehyde to acetate by the mitochondrial enzyme aldehyde dehydrogenase .
In the long run, this will generate mitochondrial dysfunction, which is considered a critical step for the
[12]
onset and progression of ALD . Dysfunctional mitochondrial can undergo a fragmentation pathway
to further be cleared by autophagy or promote the apoptotic cascade in sever liver injury by a multi-step
process called “mitochondrial dynamics” controlled by the activity of the mitochondria shaping proteins
[13]
[14]
(MSP) . In a recent study, Palma et al. demonstrated that mitochondrial dynamics showed important
changes in alcoholic steatohepatitis (ASH) patients by finding an increased expression of the MSP protein
dynamin-related protein 1 (DRP1) compared with controls. They also found a direct correlation between
DRP1 mRNA levels and blood concentration of aspartate aminotransferase in those patients. Interestingly,
this was only seen in advanced ALD subjects, suggesting the study of mitochondrial deregulation in ALD
progression is an important issue.

On the other hand, high alcohol consumption has been related with increased MEOS activity and its
first constituent, the cytochrome P-450 2E1 (CYP2E1) [15,16] . This has a great impact since, unlike the usual
dehydrogenation process, the oxidation of ethanol by MEOS is carried out through several reactive
[17]
intermediates known as reactive oxygen species (ROS) via CYP2E1 . An increase in alcohol consumption
upregulates the activity of intestinal MEOS, leading to an increase in ROS production, which interferes
[17]
with the barrier function of the gut .

MICROBIOTA AND ITS INTERACTION WITH THE INTESTINAL ENVIRONMENT
The GI tract is the natural habitat for several microorganisms, including bacteria, archaea, viruses,
and parasites. In a healthy gut microenvironment, there is a predominant diversity of seven large
groups: Firmicutes, Bacteroidetes, Actinobacteria, Fusobacteria, Proteobacteria, Verrucomicrobia, and
[18]
Cyanobacteria . The gut microbiome, which refers to the collective genomes of all the microorganisms
[18]
that compose the gut microbiota, contains 150 times more genes than the human genome . In addition,
gut bacteria has been appreciated for the benefits they can provide to the host (symbiosis) as they supply
essential nutrients such as vitamins, metabolize non-digestible compounds, and even defend against
pathogenic microorganisms [19,20] .

The colonization of the healthy gut environment contributes to the development of the intestinal
architecture and the proper functioning of the immune system. Colon bacteria can ferment nutrients and