Alcohol and the gastrointestinal tract

The small intestine: barrier, permeability and microbiota

In recent years, there has been growing interest in the comprehension of the physiology of intestinal permeability and microbiota; and how these elements could influence the pathogenesis of diseases. The term intestinal permeability describes all the processes that allow the passage of molecules as water, electrolytes and nutrients through the intestinal barrier by the paracellular or the transcellular transport systems with several implications for self-tolerance and not-self immunity. An increased permeability might induce a more significant interaction of the immune system with unknown external antigens. This might favor the onset of several immune-related extra-intestinal diseases including coeliac disease, diabetes mellitus type 1, bronchial asthma and inflammatory bowel diseases. Furthermore, the intestinal permeability interacts every day with microbiota, the complex system of mutualistic inhabitants and commensal microorganisms living in the healthy gut. Microbiota is implicated in physiological functions by actively participating in digestion, absorption, synthesis of vitamins and protection from external aggressions. The critical site where these processes occur is the small intestine to which this updated review is dedicated. Understanding its anatomy, its barrier structure and permeability modulation and its microbiota composition is the essential skill to comprehend the complex pathogenesis of several - not only gastroenterological - diseases.

Helicobacter pylori Infection and Predictors Among Dyspeptic Adult Patients in Southwest Ethiopia: Cross-Sectional Study

Background

Globally, H. pylori infection affects approximately 4.4 billion people. The burden of the infection varies within and between countries, with a higher prevalence reported from developing countries including Ethiopia. Thus, this study aimed to determine the magnitude and predictors of H. pylori infection among dyspeptic patients who visited Wachemo University Nigist Eleni Mohammed Memorial Referral Hospital, Southwest Ethiopia.

Methods

Consecutive willing dyspeptic adult patients (n=405) were enrolled in a cross-sectional study done from September to December 18, 2019. Socio-demographic and behavioral characteristics of the study participants were gathered by a pretested structured questionnaire. Stool samples were examined for H. pylori antigens using Wondfo one step H. pylori feces test kit. SPSS version 20 was utilized to compute descriptive statistics, binary and multivariate logistic regression. A p-value of <0.05 was considered statistically significant.

Results

Mean age of patients was 30 (± 7.4 SD) years, and 56.8% of participants were females. About 51.4% (208/405) of adult dyspeptic patients were infected with H. pylori. Being female gender (AOR꞊ 2.56, CI 95% ꞊1.61-4.07, p꞊0.001), consumption of alcohol (AOR꞊1.95, CI 95% ꞊1.02-3.73, p꞊ 0.019) and being undernourished (underweighted) (AOR꞊ 4.59, CI 95%꞊ 1.28-16.45, p꞊0.019) were independent predictors of H. pylori infection.

Conclusion

In the study area, high (51.4%) magnitude of H. pylori infection was observed in dyspeptic patients and significantly associated with female gender, alcohol consumption, and undernourishment.

Gut region-dependent alterations of nitrergic myenteric neurons after chronic alcohol consumption

Chronic alcohol abuse damages nearly every organ in the body. The harmful effects of ethanol on the brain, the liver and the pancreas are well documented. Although chronic alcohol consumption causes serious impairments also in the gastrointestinal tract like altered motility, mucosal damage, impaired absorption of nutrients and inflammation, the effects of chronically consumed ethanol on the enteric nervous system are less detailed. While the nitrergic myenteric neurons play an essential role in the regulation of gastrointestinal peristalsis, it was hypothesised, that these neurons are the first targets of consumed ethanol or its metabolites generated in the different gastrointestinal segments. To reinforce this hypothesis the effects of ethanol on the gastrointestinal tract was investigated in different rodent models with quantitative immunohistochemistry, in vivo and in vitro motility measurements, western blot analysis, evaluation of nitric oxide synthase enzyme activity and bio-imaging of nitric oxide synthesis. These results suggest that chronic alcohol consumption did not result significant neural loss, but primarily impaired the nitrergic pathways in gut region-dependent way leading to disturbed gastrointestinal motility. The gut segment-specific differences in the effects of chronic alcohol consumption highlight the significance the ethanol-induced neuronal microenvironment involving oxidative stress and intestinal microbiota.

Intestinal barrier function: molecular regulation and disease pathogenesis

The intestinal epithelium is a single-cell layer that constitutes the largest and most important barrier against the external environment. It acts as a selectively permeable barrier, permitting the absorption of nutrients, electrolytes, and water while maintaining an effective defense against intraluminal toxins, antigens, and enteric flora. The epithelium maintains its selective barrier function through the formation of complex protein-protein networks that mechanically link adjacent cells and seal the intercellular space. The protein networks connecting epithelial cells form 3 adhesive complexes: desmosomes, adherens junctions, and tight junctions. These complexes consist of transmembrane proteins that interact extracellularly with adjacent cells and intracellularly with adaptor proteins that link to the cytoskeleton. Over the past decade, there has been increasing recognition of an association between disrupted intestinal barrier function and the development of autoimmune and inflammatory diseases. In this review we summarize the evolving understanding of the molecular composition and regulation of intestinal barrier function. We discuss the interactions between innate and adaptive immunity and intestinal epithelial barrier function, as well as the effect of exogenous factors on intestinal barrier function. Finally, we summarize clinical and experimental evidence demonstrating intestinal epithelial barrier dysfunction as a major factor contributing to the predisposition to inflammatory diseases, including food allergy, inflammatory bowel diseases, and celiac disease.

The alcoholic lung: epidemiology, pathophysiology, and potential therapies

Epidemiological evidence gathered only in the past decade reveals that alcohol abuse independently increases the risk of developing the acute respiratory distress syndrome by as much as three- to fourfold. Experimental models and clinical studies are beginning to elucidate the mechanisms underlying this previously unrecognized association and are revealing for the first time that chronic alcohol abuse causes discrete changes, particularly within the alveolar epithelium, that render the lung susceptible to acute edematous injury in response to sepsis, trauma, and other inflammatory insults. Recent studies in relevant animal models as well as in human subjects are identifying common mechanisms by which alcohol abuse targets both the alveolar epithelium and the alveolar macrophage, such that the risks for acute lung injury and pulmonary infections are inextricably linked. Specifically, chronic alcohol ingestion decreases the levels of the antioxidant glutathione within the alveolar space by as much as 80-90%, and, as a consequence, impairs alveolar epithelial surfactant production and barrier integrity, decreases alveolar macrophage function, and renders the lung susceptible to oxidant-mediated injury. These changes are often subclinical and may not manifest as detectable lung impairment until challenged by an acute insult such as sepsis or trauma. However, even otherwise healthy alcoholics have evidence of severe oxidant stress in the alveolar space that correlates with alveolar epithelial and macrophage dysfunction. This review focuses on the epidemiology and the pathophysiology of alcohol-induced lung dysfunction and discusses potential new treatments suggested by recent experimental findings.

Protective effects of medium-chain triglycerides on the liver and gut in rats administered endotoxin

OBJECTIVE

To determine if medium-chain triglycerides (MCTs) prevent organ injuries and mortality in rats administered endotoxin and to investigate effects of MCT on the gut.

SUMMARY BACKGROUND DATA

Since dietary MCTs prevent alcohol-induced liver injury by inhibiting activation of Kupffer cells in the enteral feeding model, the authors hypothesized that MCT could prevent deleterious conditions in endotoxemia.

METHODS

After a preliminary experiment determined the optimal dose of MCT, rats were given MCT (5 g/kg per day) or the same dose of corn oil by gavage daily for 1 week. Then, lipopolysaccharide (LPS) was administered intravenously and survival was assessed for the next 24 hours. For analysis of mechanisms, rats were killed 9 hours after LPS injection and serum and liver sections were collected. To investigate effects of MCT on the gut, pathologic change, permeability, and microflora were assessed. Kupffer cells isolated by collagenase digestion and differential centrifugation were used for endotoxin receptor CD14 immunoblotting, phagocytic index, and TNF-alpha production assay.

RESULTS

All rats given corn oil died after LPS administration; however, this mortality was prevented by MCT in a dose-dependent manner. Rats given corn oil showed liver injury after LPS administration. In contrast, MCT prevented this pathologic change nearly completely. MCT blunted CD14 expression on the Kupffer cells and TNF-alpha production by isolated Kupffer cells; however, there were no differences in phagocytic index between the two groups. The length of the intestinal epithelium was increased in the MCT group compared to the corn oil group. Further, after LPS administration, increases in gut permeability and injury were prevented by MCT. Importantly, MCT also prevented hepatic energy charge and gut injuries in this condition.

CONCLUSIONS

Enteral feeding using MCT could be a practical way of protecting the liver and intestine during endotoxemia.

Mucosal biotransformation

About 4 million compounds have been described by chemists, and some 60,000 are presently on the market. The search for new chemicals with better properties and less toxicity continues, and future life quality will depend on our ability to find the safest compounds in each field of application. During development of new drugs and chemicals, studies on biotransformation should be done very early, and with adequate analytical tools, in order to get an early understanding of data on bioavailability, metabolic pattern, and toxicity. Though the liver is generally the organ with the highest drug metabolizing activity, it becomes increasingly evident that some extrahepatic organs, such as intestine, kidney, skin, and lung also participate in drug metabolism. The peculiar property of intestinal metabolism is the fact that it modifies chemicals before they enter the circulation. Therefore, an understanding of intestinal metabolism is important for proper interpretation of all pharmacological and toxicological data during development of a new compound. Mucosal biotransformation has recently been reviewed. The present work gives a schematic survey on the topic, shows new trends, and discusses the consequences for toxicological testing of new chemicals.