Microbial populations found within the GIT, have numerous roles in different aspects of human health [22]. Any change in the normal microbiome can be the cause of various diseases, including gastrointestinal cancers and obesity [23, 24]. Probiotics are externally administered living microbes that are beneficial for human health via their regulatory function on the host GI microbiome, host immune system, and systemic inflammation [25-27]. Probiotics, if administered in a sufficient amount, can improve diseases, or the lessen the complications of various disorders, including GI cancers, inflammatory bowel disease (IBD), rheumatoid arthritis, obesity, and diabetes (Table 1) [28, 29]. Lactobacillus and Bifidobacterium species are the major bacterial strains that are generally consumed as probiotics [29].
The major mechanisms of action of probiotics, include enhancement of the gut epithelial barrier, adhesion to intestinal mucosa, and concomitant inhibition of pathogen adhesion, competitive exclusion of pathogenic microorganisms, production of anti-microbial substances, and modulation of the immune system (Figure 1).
Epidemiological studies clearly show that, despite all the advances made in the field of diagnosis, prevention and treatment of cancer, the prevalence of cancer is still increasing. About 80% of all types of cancer are due to environmental and lifestyle factors [30]. Due to the high burden of cancer around the world, effective treatment cancer is very important [31]. There are many treatment methods such as chemotherapy, radiotherapy, targeted therapy and immunotherapy, but their overall efficacy is still not satisfactory [32, 33]. Probiotics have recently been used to improve cancer treatment, relieve symptoms and increase the quality of life [34]. One of the reasons for the occurrence of cancers, in particular GIT cancers, may be changes in the normal GI microbial flora, and therefore the use probiotics is attractive to modulate these changes, reduce complications, or even treat cancer [35]. In one study by Gao et al., probiotic therapy reduced the number of mucosal-associated pathogens in patients with colorectal cancer (CRC) by altering the profile of microbial flora in the mucosa. A total of 22 CRC patients completed the trial. Patients were randomized into a PGT group (n = 11) taking probiotics or CGT group (n = 11) taking preoperative placebo. It should be noted that the participants in the PGT group took an encapsulated probiotic combination consisting of living Bifidobacterium longum, Enterococcus faecalis, and Lactobacillus acidophilus (1:1:1) with at least 1×107 CFU/g viable cells, 3 times a day, with a total daily dosage of 6×107 CFU for 5 days. The participants in the CGT group took only encapsulated maltodextrin 3 times a day. The results showed that the probiotic supplement regimen could efficiently modify the composition and diversity of the gut microflora. It could also suppress specific potential pathogens such as Peptostreptococcus and Fusobacterium strains. In addition, probiotics enhanced the numbers of specific beneficial microorganisms [36]. Abnormal blood vessels and hypoxic and necrotic regions are common features of solid tumors and related to the malignant phenotype and therapy resistance. Certain obligate or facultative anaerobic bacteria exhibit inherent ability to colonize and proliferate within solid tumors in vivo. Escherichia coli Nissle 1917, a non-pathogenic probiotic in European markets, has been known to proliferate selectively in the interface between the viable and necrotic regions of solid tumors. Li et al. established a tumor-targeting therapy system using the genetically engineered E. coli Nissle 1917 for targeted delivery of cytotoxic compounds, including glidobactin, colibactin, and luminmide. Biosynthetic gene clusters of these cytotoxic compounds were introduced into E. coli Nissle 1917 and the corresponding compounds were detected in the resultant recombinant strains. The recombinant E. coli Nissle 1917 showed cytotoxic activity in vitro and in vivo as well, and suppressed the tumor growth [37]. Another study was conducted to evaluate the effect of probiotic supplementation in patients with laryngeal cancer. After the intervention, biochemical markers of stress were reduced. A total of 20 healthy controls and 30 patients with laryngeal cancer were included. Then, for two weeks prior to the surgical operation, 20 patients were randomly assigned to take a placebo or probiotic supplement (Clostridium butyricum; 420 mg/capsule) two times per day. In addition, the degree of anxiety and the heart rate were assessed. It was found that the level of serum corticotropin‐releasing factor (CRF) in patients with laryngeal cancer was increased as they approached the time of surgery, but no corresponding increase in CRF, anxiety or heart rate was seen after probiotic use. Probiotics reduced the level of the patient anxiety on the Hamilton Anxiety Scale (HAMA) from 19.8 to 10.2. Consequently, clinical anxiety and biochemical features of stress were decreased by probiotics administration in the participants assigned for laryngectomy [38]. In another study carried out on patients with gastric cancer, the results showed that the combination of dietary fiber and probiotics was effective in treating post-operative diarrhea. The study included 120 patients suffering from GC. Patients were assigned to one of 3 groups as follows: (1) Fiber-enriched nutrition formula (FE group, n = 40), (2) Fiber-free nutrition formula (FF group, n = 40), and (3) Fiber and probiotic-enriched nutrition formula, a combination of live bifidobacterium and lactobacillus in tablets , (FEP group, n = 40). Then, each patient received enteral nutrition (EN) formulae for seven successive days after the surgical operation [39]. Earlier investigations had shown that addition of the fiber or probiotics may preserve the intestinal microecology, and diminish diarrhea related to EN [40]. Dietary fiber is a kind of carbohydrate polymer, which cannot be digested by humans. Some researchers have shown that the effects of combined probiotics and fiber on the treatment of diarrhea were indecisive [41-43]. According to the present RCT investigation, the combination of probiotics and fiber may reduce diarrhea, augment intestinal motility, and diminish intestinal dysfunction in the post-operative GC patients receiving EN. Additionally, probiotics may shorten the length of hospital stay (LOHS) as part of enhanced recovery after surgery (ERAS) protocols. Therefore, the combination of fiber and probiotics when beginning EN, may avoid diarrhea related to EN, improving comfort, and enhancing recovery after surgical operation [39].
Ventilator-associated pneumonia (VAP) is often caused by aspiration of pathogenic bacteria from the oropharynx. Oral decontamination by using antiseptics, such as antibiotics or chlorhexidine (CHX), can be used as prophylaxis. Klarin et al. examined the probiotic effect of bacteria Lactobacillus plantarum 299 (Lp299) as CHX in reducing the pathogenic bacteria in the oropharynx. Fifty tracheally intubated, mechanically ventilated, critically ill patients critically ill patients administrated to either oral cleansing by 0.1% CHX solution or to the same washing procedure and oral using of an emulsion of Lp299. Oropharynx samples showed that pathogenic bacteria that were not present at inclusion were detected in the patients treated with Lp299 was less than those in control group [44].
Inflammatory bowel disease (IBD) consists of two disorders, Crohn's disease and ulcerative colitis [45]. In the pathogenesis of IBD, it is thought that pathogenic or resident luminal bacteria continuously activate the mucosal and systemic immune systems, and ultimately cause an inflammatory cascade [46]. IBD is a chronic immunological disease that is related to lack of dietary fiber, saturated fatty acids, poor sleep, and low levels of vitamin D in the body [45]. For medical therapy, drugs such as immunomodulators and 5-aminosalicylic acid (5-ASA) can be used [47]. Antibiotics and probiotics are also used to treat IBD [48]. So far, several studies have been performed to evaluate the efficacy of probiotics in IBD. In one study carried out by Shadnoush et al., supplementation with probiotics improved intestinal function in patients with IBD. A total of 305 participants were classified into 3 groups. Group A (IBD patients taking probiotic yogurt (contained Lactobacillus acidophilus La-5 and Bifidobacterium BB-12): n = 105), group B (IBD patients taking a placebo: n = 105), or control group (healthy persons taking probiotic yogurt: n = 95). Stool samples were obtained before and after eight weeks of intervention. Afterwards, the numbers of Bifidobacterium, Lactobacillus, and Bacteroides species in the stool samples were measured. It was found that the mean number of Bifidobacterium, Lactobacillus, and Bacteroides CFU in group A was increased compared to group B. Moreover, the mean number of all 3 bacteria was significantly different between groups A and B compared to healthy control group C. The differences between the two groups were seen both at the base-line and the completion of the study. It has been found that consuming probiotic yogurt by IBD patients can contribute to the improved intestinal function via enhancing the numbers of the beneficial bacteria in the gut. Nonetheless, it is still necessary to do more studies to confirm this concept [49]. In one study that used a Lactobacillus reuteri rectal infusion in children with chronic ulcerative colitis (UC), mucosal inflammation and the expression of some pro-inflammatory cytokines was decreased. Oliva et al. investigated the effects of a Lactobacillus (L) reuteri ATCC 55730 enema on children with active distal UC, and measured inflammation and cytokine expression in the rectal mucosa. In a prospective, randomized, placebo-controlled trial, in addition to taking oral mesalazine, the patients (n=40) received an enema solution containing 1010 CFU of L. reuteri or placebo for eight weeks. The Mayo score (endoscopic and clinical characteristics) was considerably reduced in the L. reuteri group in comparison to the placebo. Moreover, histological scores showed a considerable decline in the L. reuteri group. In addition, at the post-trial assessment of the level of mucosal cytokine expression, the anti-inflammatory IL-10 was significantly increased, while the pro-inflammatory TNFα, IL-8 and IL-1β were reduced in the L. reuteri group [50].
Kekkonen eta l. investigated production of cytokine in human peripheral blood mononuclear cells (PBMC) in response to stimulation with probiotic bacteria including Streptococcus thermophilus THS, Lactobacillus rhamnosus GG (ATCC 53103), Lactobacillus rhamnosus Lc705 (DSM 7061), Lactobacillus helveticus 1129, Lactobacillus helveticus Lb 161, Bifidobacterium longum 1/10, Bifidobacterium animalis ssp. lactis Bb12, Bifidobacterium breve Bb99 (DSM 13692), Lactococcus lactis ssp. cremoris ARH74 (DSM 18891), Leuconostoc mesenteroides ssp. cremoris PIA2 (DSM 18892) and Propionibacterium freudenreichii ssp. shermanii JS (DSM 7067). All of examined bacteria could induce TNF-α production. Streptococcus and Leuconostoc induced Th1 type cytokines IL-12 and IFN-γ more than other. All Propionibacterium and Bifidobacterium strains induced higher IL-10 production. They showed that Leuconostoc mesenteroides ssp. cremoris and Streptococcus thermophilus are more potent inducers of Th1 type cytokines IL-12 and IFN-γ than the probiotic Lactobacillus strains [51].
Atopic dermatitis (AD) is an inflammatory skin disease can be due to the imbalance between Tcell-related immune responses. Sheikhi et al. investigated the effects of lactobacillus Bulgaricus in the yogurt culture on the secretion of Th1/Th2/Treg type cytokines by PBMCsin 20 children with AD. Results showed that L. Delbrueckii subsp. Bulgaricus significantly up-regulated the secretion of IL-10, IL-12 and IFN-γ, while secretion of IL-4 was decreased by PBMCs compared to control [52].
Some studies have suggested that arthralgia is a common extra-intestinal manifestation of IBD. It is possible that disturbing the immune profile within the gut plays a role in the pathogenesis of arthralgia. A study by Karimi showed that administration of probiotics (VSL#3) could improve pouchitis in IBD patients. The safety and efficacy of VSL#3 administration for 2 weeks in patients with quiescent IBD also suffering from arthralgia, was assessed in an open-label trial. The pre-treatment and post-treatment intensity of joint pain was measured using a visual analog scale and the Ritchie Articular Index. Moreover the Truelove-Witts and the Harvey-Bradshaw scores were used to assess severity of IBD symptoms. 16 of 29 patients completed the trial. 10 of these 16 patients showed a remarkable improvement in joint pain using the Ritchie Articular Index. No patients suffered a relapse of intestinal disease while on probiotics. The above results indicated that the probiotic supplement VSL#3 could be a good therapeutic option for arthralgia inpatients suffering from IBD. Since probiotics can also serve as an IBD treatment, patients suffering from comcomitant arthralgia could take advantage of a dual treatment modality [53]. Another study carried out in laboratory dogs suggested that the anti-inflammatory effects of probiotic administration could be due to reduced mucosal immune cell infiltration, accompanied by increased levels of putrescine (PUT), ornithine decarboxylase (ODC) and diamino-oxidase (DAO), which play an anti-inflammatory role [54].
Irritable bowel syndrome (IBS) is a common chronic disease of the GIT with an incidence of 3 - 20 % in the US [55, 56]. The exact mechanisms of IBS pathogenesis are still not fully understood, but immunological disturbances and low levels of inflammation contribute to the symptoms of the disease [57]. IBS is a complex of different symptoms, such as abdominal pain, diarrhea, constipation, and general bodily weakness [55]. The main treatments are drug therapy with anti-spasmodic and anti-diarrheal drugs, fiber-rich diet for constipation, and supportive treatment with low dose antidepressants [55]. In addition to these treatments, probiotics can also be used to treat IBS; Nevertheless the role of probiotic microorganisms in the treatment of IBS has not yet been fully confirmed [58]. Several studies have shown the reduction of IBS symptoms by probiotic administration; however, there is still not enough evidence about their impact on psychiatric comorbidity. For example, Pinto-Sanchez et al. carried out a prospective study to evaluate the effects of Bifidobacterium longum NCC3001 (BL) on depression and anxiety symptoms in patients suffering from IBS. The researchers randomly selected 44 IBS patients suffering from diarrhea for the trial. The patients took either BL (n=22) or placebo (n=22) for 6 weeks. Afterwards, the levels of depression and anxiety, IBS symptoms, quality of life (QOL), and somatization were measured at weeks 0, 6, and 10. This study demonstrated a reduction in depression by probiotic BL; however, they observed no reduction in the anxiety scores. Moreover, the probiotic BL increased QOL in IBS patients. They found a correlation between the psychological improvements and changes in the brain activation pattern, indicating a reduction in limbic reactivity by probiotics [59]. Mezzasalma et al. investigated the efficacy of a supplementary regimen containing multi-species probiotics to alleviate patient IBS symptoms, such as constipation (IBS-C), and also measured their gut microbiota. They conducted their study in 150 IBS-C participants who received orally administered probiotic mixtures F_1 or F_2 or else placebo F_3 for 60 days. The results showed that the improvement in symptoms was greater in the probiotic group in comparison with the placebo group. The symptoms also remained in remission during the follow-up period. Moreover, fecal analyses showed that the probiotics enhanced fecal bacterial DNA in participants who received F_1 and F_2, but not with F_3. A similar level continued during the follow-up course. [60]. In another study, Choi et al. explored the effectiveness of a combined treatment with mosapride and probiotics in IBS patients without diarrhea. They randomly assigned 285 IBS patients to receive over 4 weeks, a combined treatment with probiotics (Streptococcus faecium & Bacillus subtilis) plus mosapride at 4 different dosages (groups 1-4), or a placebo. The proportion gaining AR at the fourth week was greater in all treatment groups in comparison with the placebo group. Moreover, the proportion of the patients who improved on the SGA was also greater in the treatment groups compared to the placebo group. In addition, abdominal discomfort and pain scores in treatment group 4 showed the best improvement in comparison to the placebo group. In patients suffering from constipation-predominant IBS, greater improvement was observed in stool frequency and consistency in the treatment groups 4 and 1 as compared to the placebo group[61].
Celiac disease (CD) is a chronic immune-mediated disease caused by the consumption of foods containing gluten, especially wheat, and is most often seen in genetically-predisposed individuals [62]. The part of the intestines involved in CD is the proximal section of the small intestine [63]. The prevalence of celiac disease is different worldwide, but its incidence has increased in the last few decades [64]. Currently, the only effective treatment for patients with CD is a gluten-free diet (GFD) [65]. Of course, the effectiveness of this treatment depends on the strict avoidance of gluten, which may sometimes be difficult [65]. In patients with celiac disease, as compared to healthy people, the beneficial gut microbes have been shown to be decreased, and the potentially pathogenic microbes are increased [66]. This change in the microbiome increases the inflammatory response in the intestine and worsens celiac disease [66]. Considering the role of probiotics in modulating microbial populations, probiotics could be used to reduce inflammatory response and to improve the symptoms of celiac disease. In a study evaluating the effects of Bifidobacterium infantis Natren Life Start (NLS) strain super strain in patients with CD, it was concluded that this strain could relieve the symptoms of untreated individuals. 22 patients who were positive for two different CD-specific tests were enrolled in this study. The patients were randomly assigned to take two capsules before meals for three weeks, containing either placebo or Bifidobacterium infantis super strain (Lifestart 2). It was found that B. infantis alleviated the symptoms in the untreated CD patients. Moreover, probiotics produced a number of immunologic alterations, but the abnormal intestinal permeability was not affected [67]. Another study conducted by Olivares et al. used Bifidobacterium longum CECT 7347 in children with newly diagnosed CD, showed that this probiotic could improve the QOL in subjects. They assessed the effects of oral administration of the B. longum CECT 7347 in 33 children who were diagnosed with CD, after they had been on a gluten-free diet (GFD) for a three-month period. It was concluded that oral administration of B. longum CECT 7347 in combination with a GFD decreased the potentially pro-inflammatory bacteria in the gut (B. fragilis group) which have been associated with CD in earlier studies, as well as fecal sIgA (soluble immunoglobulin A). In addition, B. longum CECT 7347 decreased activated T-lymphocytes and inflammatory markers (TNF-a), possibly showing improved immune homeostasis in CD patients [68]. Another study that investigated the effects of a probiotic consisting of two strains Bifidobacterium breve BR03 and B. breve B632 in children with CD combined with a GFD, showed that the TNF-α inflammatory cytokine was decreased in these children after the intervention [69]. In vitro investigations also showed that several strains of Bifidobacteria could lower levels of pro-inflammatory cytokines (TNF-α, IFN-γ, & IL-2) and increase levels of the anti-inflammatory cytokine (IL-10). Bifidobacteria may be able to reverse the pro-inflammatory milieu caused by the microbiota of patients with CD [70-72]. Moreover, many researchers have shown that B. breve strains can exert immuno-modulatory effects both in vitro and in vivo [73, 74]. It has been established that these probiotics bacteria possess the Qualified Presumption of Safety status [75]. Two recent studies have shown that intestinal inflammation can be prevented by B. breve strains via induction of a population of T-regulatory 1 (Tr1) cells that secrete IL-10 [76, 77]. It is possible that gliadin-specific Tr1 cell clones could suppress the proliferation of pathogenic T-cells in CD patients [78]. Autoimmune-type dysfunction in known to be increased in CD patients [79]. Supplementation with B. breve probiotics plus a GFD can ameliorate the pro-inflammatory environment in the CD gut, and thus reduce the recurrence of the disease. In another study, Klemenak et al. determined the effects of a combined treatment with B. breve strains B632 and BR03 plus a GFD on the immunological function of CD children by measuring serum levels of TNF-a and IL-10. They randomly assigned 49 CD children on a GFD into treatment and placebo groups, plus 18 healthy children in a control group. The first group (24 CD children) took B. breve strains BR03 and B632 (2×109 colony-forming units) per day, while the second group (25 CD children) took a placebo for three months. The results showed a significant reduction in the level of TNF-α in the first group after the administration of B. breve for three months. Follow-up three months after the end of the study showed that level of TNF-α increased once again. The levels of IL-10 were below the detection level in each group. They concluded that probiotic B. breve strains could decrease the proinflammatory cytokine TNF-a in CD children on a GFD [80]. Quagliariello et al. also found that a supplement of Bifidobacterium breve (B632 and BR03) in CD children treated with GFD could increase the amount of beneficial microbial compounds in the gut [81].
In a study the response of intestinal epithelial cells to Enterococcus faecium NCIMB 10415 (E. faecium) and two pathogenic E. coli strains was examined, with focus on the probiotic modulation of the response to the pathogenic challenge. Intestinal cells (IPEC-J2 and Caco-2) were incubated without bacteria (control), with E. faecium, with enteropathogenic (EPEC) or enterotoxigenic E. coli (ETEC) each alone or in combination with E. faecium. Results showed that the ETEC strain decreased transepithelial resistance (TER) and increased IL-8 mRNA and protein expression in both cell lines compared with control cells, an effect that could be prevented by pre- and coincubation with E. faecium. Similar effects were observed for the increased expression of heat shock protein 70 in Caco-2 cells. When the cells were challenged by the EPEC strain, no such pattern of changes could be observed. The reduced decrease in TER and the reduction of the proinflammatory and stress response of enterocytes following pathogenic challenge indicate the protective effect of the probiotic. [82]
Rheumatoid arthritis (RA) is the most common type of inflammatory arthritis, and is a main cause of disability [83]. Inflammatory cytokines play an important role in the pathogenesis of RA. An imbalance between pro-inflammatory and anti-inflammatory cytokines causes induction of autoimmunity and chronic inflammation resulting in joint damage [84]. Epidemiological studies have estimated a 0.5-1% prevalence worldwide, and an annual average incidence of 0.02-0.05% in the Northern European and North American regions [85]. There are several drugs given to patients with RA, one of which is methotrexate (MTX) [86]. However all of these drugs have side effects that can adversely affect the QOL of RA patients. For example, MTX commonly causes GI symptoms and elevation of hepatic enzymes, while severe hemocytopenia and MTX pneumonitis occur less frequently [87]. Given the role that probiotics play in down-regulating inflammatory cytokines [88], they could be substituted for drugs in the treatment of RA. In a study by Mandel, supplementation with Bacillus coagulans GBI-30 was shown to be effective in patients with RA [89]. A probiotic mixture of three strains of Lactobacillus acidophilus, Lactobacillus casei and Bifidobacterium bifidum was given for 8 weeks to patients with RA. Probiotics showed positive effects on serum insulin levels, assessment of B cell function (HOMA-B), and serum high-sensitivity C-reactive protein (hs-CRP) concentrations in a study by Zamani et al [90]. Another study was conducted to investigate the effects of Lactobacillus casei 01 in RA patients. At the end of the intervention it was found that this strain could reduce the symptoms of this disease. The researchers randomly assigned women with established RA to receive either a placebo or one capsule containing 108 colony-forming units (CFU) of L. casei 01 for eight weeks. Serum levels of cytokines IL-1β, IL-10, IL-6, TNF-α and IL-12 were measured. They concluded that L. casei 01 could decrease the serum level of hs-CRP, improve swollen joints and tenderness, and increase the global health score and disease activity score-28 (P < 0.05). They showed a significant difference between both groups for IL-12, IL-10, and TNF-α levels over the study (P<0.05), in favor of the probiotic group. There were no adverse effects in the intervention group. They concluded that probiotics could be a useful supplement for patients with RA, to alleviate symptoms and reduce inflammatory cytokines [91]. In a study by Hatakka et al. supplementation with Lactobacillus rhamnosus GG (LGG) reduced the severity of RA. However, probiotic therapy with Lactobacillus GG showed no effects on RA severity. Therefore, it is necessary to do more research into probiotic bacteria for RA patients [92].