Review/Oorsig Volume 23, Issue 01 - Page 14

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