Oorsig/Review
proglucagon mRNA, and reduced intestinal
expression of the pattern recognition receptors
CD-14 and NOD1. It also leads to a reduction
in the circulating level of lipopolysaccharide
and an increase in glucagon-like peptide1.
In addition, probiotic-treated mice have
shown increases in lipoproteinlipase-dependent
triglyceride storage in adipose tissue and
adipocyte triacylglycerol accumulation [25, 53].
Probiotic Lactobacillus strains have been found to
increase gastrointestinal barrier function by the
proliferation of harmful bacteria in nonalcoholic
fatty acid liver diseases and IBD [15, 24].
An accumulating body of research on probiotics
provides evidence that T regulatory (Treg)
cells play a crucial role in maintaining
immune homeostasis in many diseases. Treg
cells secrete IL-10, IL-17, and IL-22 (anti-
inflammatorycytokine) which are important for
maintenance of homeostasis [54–56]. Commensal
Lactobacillus species can restore homeostasis in
intestinal disorders and thus play a protective
role against inflammatory diseases.
A recent study showed that a probiotic species
of Lactobacillus acidophilus (L. acidophilus)
administered for modulation of dextran sulfate
sodium-induced colitis restored the balance of
inflammatory cytokines and T17/Treg cells [15].
The authors also reported that L. acidophilus
suppressed proinflammatory cytokines such
as IL-6, tumor necrosis factor-a, and IL-1b in
colon tissues. In addition, in vitro treatment by
L. acidophilus directly induced the production of
IL-10 and Treg cells and suppressed the
production of IL-17. Similarly, a probiotic strain
of L. acidophilus isolated from a normal human
intestinal tract and orally administrated in mice
with dextran sulfate sodium-induced colitis
suppressed the colitis-associated response of
the IL-23/T17 axis and reduced the secretion of
proinflammatory cytokines [17].
Furthermore, based on Treg cell modulation
and T17-biased immune response in regulatory
cytokines, the probiotic strain of Lactobacillus spp.
showed beneficial effects in preventing cancer and
intestinal infammation [16, 19, 57, 58]. Similarly,
a probiotic strain of L. plantarum TN8 reduced the
proinflammatory cytokine expression and also
regulated the intestinal immune system of Wistar
rats with trinitrobenzene sulfuric acidinduced
colitis [59]. The same probiotic strains
(L. plantarum TN8) also showed anti-
inflammatory properties by inducing production
of IL-10 and a small amount of IL-12 cytokines
[60].
14
4.2.Bifdobacterium.
Bifidobacterium
is
important in gut microbiota studies and has
long been used as a probiotic to alleviate
various diseases by changing the gut microbiota
composition.
Like
other
Lactobacillus,
Bifidobacterium can also inhibit harmful bacteria,
improve gastrointestinal barrier function, and
suppress proinflammatory cytokines [24].
Recent studies have demonstrated that
Bifidobacterium alters the function of dendritic
cells to regulate the intestinal immune
homeostasis to harmless antigens and bacteria or
initiate protective measures against pathogens. It
also has the potential to control various intestinal
diseases, like IBD, cancer, and allergies [61–
63]. The probiotic Bifidobacterium has shown
metabolic capacity in gut bacteria and can increase
the proportion of beneficial bacteria in the gut
microbiota by cross-feeding. According to Turroni
et al. [64], Bifidobacterium bifdum significantly
increased metabolic activity when cocultured
with Bifidobacterium breve. This coculture of
probiotic bacteria affected the metabolic shif in
the gut microbiota by increasing the production
of shortchain fatty acids rather than by changing
the gut microbiota composition. Colonic mucus is
a physical barrier that consists of gut microbiota
and is maintained by an extensively glycosylated
mucin-2 network. In vivo, the ability of bacteria-
sized beads to penetrate the mucus layer was
greater in mice fed a Western-style diet than in
chow-fed mice, which indicated slower mucus
growth in the mice fed a Western-style diet due to
host metabolic factors. It is worth noting that the
abundance of Firmicutes increased and that of
Bacteroidetes and Actinobacteriawere reduced
in the colonic lumen of mice fed a Western-
style diet. A study with probiotic treatment
showed that Bifidobacterium longum NCC 2705
(B. longum) prevented mucus production [65].
Moreover, Bifidobacterium exerts a positive
efect via hormonal signalling in the gut-brain
microbiome axis to improve memory function,
including brain-derived neurotropic factor and
N-methyl-D-aspartate receptor expression. It has
been reported that a combination of Lactobacilli
and Bifidobacterium decreased acute stress and
depression [66, 67]. However, the understanding
of the molecular mechanism is beyond the scope
of this study.
4.3. Other Bacteria Species. Like other probiotic
species, Escherichia coli, a gram-negative
bacterium in the Enterobacteriaceae family,
is a well-known probiotic strain with some
beneficial effects on gut microbiota homeostasis.
The nonpathogenic strain Escherichia coli Nissle
(EcN) is one of the most used probiotic strains