Tehran University Medical Journal

Background: Colorectal cancer is the second most common cancer in the world which is mainly caused by epigenetic and environmental factors. Among these epigenetic factors, gut microbiota is an important one. Although it has not been proved a unique group of bacteria correlated with colorectal cancer, these findings have generally demonstrated differences between healthy and disease gut microbiome in population. Actually, the identification and investigation of intestinal microbiota in early detection of colorectal cancer have been highlighted in new researches and studies. Herein, in the current study, we aimed to evaluate the number of selected gut bacteria including Lactobacillus and Escherichia coli and Prevotella in the fecal specimens of adenomatous polyposis patients, colorectal cancerous cases in compared to normal participants in terms of estimating important role of gut microbiota during colorectal cancer initiation and progression.
Methods: The current research was a case-control study. Fecal samples were provided from 31 healthy individuals, 42 adenomatous polyposis patients and 20 colorectal cancer cases that were referred to Taleghani Hospital, Tehran, Iran, from August 2016 to August 2017 for colorectal cancer screening tests. Fecal samples were collected to analyze intestinal bacteria including, Lactobacillus, Escherichia coli, and Prevotella by absolute quantitative real-time polymerase chain reaction (PCR). The number of these gut bacteria was precisely determined by this method of real-time PCR.
Results: Higher number of Prevotella with 24.6 CT number (P<0.005) and E.coli with 20.4 CT number (P<0.015) were achieved in colorectal cancer cases and adenomatous polyposis patients in contrast to samples from normal individuals. On the contrary, the opposite range was observed for the quantification of Lactobacillus and greater numbers of bacteria (CT=28.6) were detected in normal, compared to the colorectal cancer cases and adenomatous polyposis (P<0.001).
Conclusion: The gut microbiota composition of individuals with colorectal cancer and adenomatous polyposis differs from that of healthy individuals, and the higher numbers of pathogenic microbiota versus beneficial microbiota present in those with colorectal cancer and adenomatous polyposis. In contrast, healthy individuals have higher numbers of beneficial gut microbiota than pathogenic microbes. These findings need more experimental analysis and investigation to better clarify.

Inflammatory bowel disease (IBD) is a chronic, relapsing gastrointestinal disorder characterized by persistent inflammation of the intestinal mucosa, disruption of epithelial barrier function, and dysregulation of the immune system. Its pathogenesis involves complex interactions among genetic predisposition, environmental factors, gut microbiota, and host immune responses. Dysregulated cytokine signaling plays a central role, with elevated levels of pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), IL-6, IL-12, and interferon-gamma (IFN-γ), contributing to tissue damage, epithelial barrier dysfunction, and clinical manifestations such as diarrhea, bleeding, and weight loss. Conversely, anti-inflammatory cytokines, including interleukin-10 (IL-10), IL-35, and IL-37, counteract these inflammatory responses, inhibit excessive immune activation, and maintain mucosal homeostasis. Probiotics, particularly Lactobacillus strains, have emerged as promising adjunctive therapies for IBD due to their capacity to restore microbial balance, modulate immune responses, and enhance gut barrier integrity. Among them, Lactobacillus brevis has demonstrated significant immunoregulatory and anti-inflammatory effects. Various strains, including AL0035, SBC8803, Bmb6, HY7401, and KU15152, reduce pro-inflammatory cytokines, upregulate tight junction proteins such as ZO-1, regulate Th1/Th2/Th17 responses, and inhibit NF-κB and MAPK signaling pathways. L. brevis-derived metabolites, notably long-chain polyphosphates, attenuate fibrosis, reduce TGF-β1 and collagen expression, and protect epithelial cells from oxidative stress. Heat-killed L. brevis strains also retain immunomodulatory activity, allowing therapeutic use even when live bacteria cannot effectively colonize the gut. Preclinical studies demonstrate that oral administration of L. brevis improves disease activity indices in experimental colitis models, reduces mucosal immune cell infiltration, restores epithelial integrity, and prevents ulceration, bleeding, and goblet cell depletion. Clinical evidence, although limited, suggests that L. brevis supplementation can enhance gut microbiota diversity, increase beneficial bacterial populations, and modulate serum cytokines, further supporting intestinal homeostasis. Furthermore, L. brevis influences metabolite profiles, such as serotonin and polyamines, which are linked to gut motility, epithelial repair, and immune regulation, highlighting its multifaceted role in gut health. In this review article, for the first time, we discussed the beneficial effects of L. brevis in inflammatory bowel disease, highlighting its clinical effects and therapeutic prospects.