Investigation Of The Underlying Mechanisms Of LGGS's Protective Role In ALD

ALD (Alcoholic liver disease) is defined as a broad spectrum of diseases including hepatic steatosis, fibrosis and cirrhosis, which has a high morbidity and mortality worldwide. Although a large number of studies focusing on the prevention and treatment of ALD have been carried out in the past decades, there is still no widely accepted, FDA (Food and Drug Administration) approved therapy for any stage of ALD. With the increasing recognition of the importance of gut microbiota in the onset and development of a variety of diseases, the potential use of probiotics in ALD is receiving investigative and clinical attention. Recent studies indicate that ALD is closely correlated with gut bacterial overgrowth and dysbiosis, intestinal barrier dysfunction and increased endotoxemia.Probiotics are defined as live microorganisms, when sufficient amounts of probiotics reach the intestine in an active state, they exert positive health effects. Early studies have showed that LGG (Lactobacillus rhamnosus GG) can inhibit the overgrowth of harmful gut bacteria, repair damaged intestinal barrier function, thereby inhibit alcohol-induced endotoxemia and liver damage. Generally, probiotics are considered safe, but several reports have raised safety concerns about ingesting such large amounts of bacteria, especially when the intestinal function and the patient's immune response are compromised.In this thesis, the underlying mechanisms of the protective role of LGGs (Lactobacillus rhamnosus GG supernatant) in ALD were investigated. A chronic ethanol mice model was used to explore the effects of LGGs on liver under alcohol consumption. The results showed that LGGs can effectively alleviate alcohol induced liver steatosis and hepatic kupffer cell activated inflammatory responses. Results from the intestine analysis revealed the protective role of LGGs in gut integrity. Furthermore, using human colon carcinoma cell line Caco-2 cell line, the underlying mechanisms of LGGs's protection on gut barrier function were also investigated. The results showed that LGGs exert an inhibition effect on miR122a which can increase the expression of occludin, one of the most important intestinal tight junction proteins, thus strengthen the intestinal barrier function and protect the liver.In addition, previous work in the lab have shown that alcohol consumption decrease the expression of HIF (Hypoxia-inducible factor), the key transcription factor involved in cell hypoxic response, resulting in the reduction of HIF-mediated mucosal related protein ITF (Intestinal trefoil factor), leading to an impaired gut barrier. LGGs treatment can effectively block these deleterious effects. Based on this, the functions of ITF and cathelin-related antimicrobial peptide (CRAMP), two major transcriptional targets of HIF were further explored. ITF was showed to effectively inhibit PAF (Platelet activating factor) induced increasing of epithelial permeability, while CRAMP showed a selective antimicrobial activity in the growth of pathogenic bacterial strains like Enteropathogenic E.coli and L.monocytogenes, compared to probiotic LGG.Additionally, the present work also investigated the role of butyrate, one of the SCFA (Short chain fatty acids), which are the metabolites of certain probiotics. NaB (Sodium butyrate) can significantly enhance the iron chelator DFO (desferrioxamine) induced upregulation of HIF expression, suggesting that probiotics may exert their beneficial effects through secreting these metabolites. The results in this study is of great value for a better understanding of the pathogenesis of ALD and the underlying mechanisms of probiotics' protective effects on ALD.