Dissolution of lipids from mucus: a possible mechanism for prompt disruption of gut barrier function by alcohol

Acute and/or chronic alcohol ingestion has been shown to exacerbate the morbidity and mortality rate associated with acute mechanical and/or thermal trauma. While alcohol ingestion can affect many organs and systems, clinical and preclinical studies indicate that alcohol ingestion can cause a 'leaky gut' syndrome which in turn contributes to infection and systemic organ dysfunction. This study investigated the acute effect of alcohol on gut barrier function. Using an in vivo isolated gut sac model of naïve male rats, each individual gut sac was injected with different concentrations (0, 5, 10, 20, and 40%, v/v) of alcohol. After different times of alcohol exposure, each isolated gut segment was harvested and intestinal permeability and mucosal surface hydrophobicity (a physiologic marker of mucus barrier function) were measured as well as luminal DNA, mucus, protein and free fatty acids. The results showed that alcohol caused dose-dependent and time-dependent increases in gut permeability and decreases in mucosal surface hydrophobicity, with significant changes to be observed 5 min after treatment with 10% alcohol. In addition, it is further found that these changes in permeability and hydrophobicity are more closely associated with increased intestinal luminal free fatty acids levels but not protein or DNA levels. These results suggest that alcohol may cause loss of gut barrier function by extracting and dissolving lipids from the mucus with a resultant decrease in mucosal surface hydrophobicity, which is a critical component of gut barrier function.

Moderate ethanol ingestion and cardiovascular protection: from epidemiologic associations to cellular mechanisms

While ethanol intake at high levels (3-4 or more drinks), either in acute (occasional binge drinking) or chronic (daily) settings, increases the risk for myocardial infarction and stroke, an inverse relationship between regular consumption of alcoholic beverages at light to moderate levels (1-2 drinks per day) and cardiovascular risk has been consistently noted in a large number of epidemiologic studies. Although initially attributed to polyphenolic antioxidants in red wine, subsequent work has established that the ethanol component contributes to the beneficial effects associated with moderate intake of alcoholic beverages regardless of type (red versus white wine, beer, spirits). Concerns have been raised with regard to interpretation of epidemiologic evidence for this association including heterogeneity of the reference groups examined in many studies, different lifestyles of moderate drinkers versus abstainers, and favorable risk profiles in moderate drinkers. However, better controlled epidemiologic studies and especially work conducted in animal models and cell culture systems have substantiated this association and clearly established a cause and effect relationship between alcohol consumption and reductions in tissue injury induced by ischemia/reperfusion (I/R), respectively. The aims of this review are to summarize the epidemiologic evidence supporting the effectiveness of ethanol ingestion in reducing the likelihood of adverse cardiovascular events such as myocardial infarction and ischemic stroke, even in patients with co-existing risk factors, to discuss the ideal quantities, drinking patterns, and types of alcoholic beverages that confer protective effects in the cardiovascular system, and to review the findings of recent experimental studies directed at uncovering the mechanisms that underlie the cardiovascular protective effects of antecedent ethanol ingestion. Mechanistic interrogation of the signaling pathways invoked by antecedent ethanol ingestion may point the way towards development of new therapeutic approaches that mimic the powerful protective effects of socially relevant alcohol intake to limit I/R injury, but minimize the negative psychosocial impact and pathologic outcomes that also accompany consumption of ethanol.

Ethanol induced NF-{kappa}B activation protects against cell injury in cultured rat gastric mucosal epithelium

Ethanol is a well-established irritant inducing inflammation in gastric mucosa, but the effects at the cellular level remain unclear. This study investigates NF-kappaB activation in gastric mucosal cells by ethanol and assesses the effects of heat shock pretreatment in this ulcerogenic situation. Rat gastric mucosal epithelia were exposed to ethanol for different time periods. Heat shock was induced by incubating the cells at 42 degrees C for 1 h prior to the experiments. For evaluation of NF-kappaB activation, the nuclear fraction of the cell lysates was analyzed with an EMSA or an ELISA-based assay. Caspase-3 (a promoter of apoptosis) activity was measured with a time-resolved fluorescence based assay, cell viability with a tetrazolium assay, and cell membrane integrity with a LDH assay. Ethanol (1-5%) induced NF-kappaB activation, reaching a maximum after 3 h, and also led to moderately increased COX-2 expression. Heat shock pretreatment and the intracellular calcium chelator BAPTA were able to inhibit ethanol-induced NF-kappaB activation. Heat shock pretreatment decreased ethanol-induced caspase-3 activation, decreased cell membrane damage, and retained cellular viability. Inhibition of NF-kappaB activation by NEMO-binding peptide, by decreasing RelA expression, or by inhibiting COX-2 activity by CAY-14040 promoted the effects of ethanol, such as increased caspase-3 activity and decreased cell viability. In conclusion, ethanol induces NF-kappaB activation via a calcium-dependent pathway and induces COX-2 expression. Inhibition of the NF-kappaB activation or COX-2 activity potentiates apoptosis and cell damage induced by ethanol, suggesting a protective role for NF-kappaB activation and COX-2 expression.

Animal models and their results in gastrointestinal alcohol research

Alcohol-induced diseases of the gastrointestinal tract play an important role in clinical gastroenterology. However, the precise pathophysiological mechanisms are still largely unknown. Alcohol research depends essentially on animal models due to the fact that controlled experimental studies of ethanol-induced diseases in humans are unethical. Animal models have already been successfully applied to disclose and analyze molecular mechanisms in alcohol-induced diseases, partially by using knockout technology. Because of a lack of transferability of some animal models to the human condition, results have to be interpreted cautiously. For some alcohol-related diseases like chronic alcoholic pancreatitis, the ideal animal model does not yet exist. Here we provide an overview of the most commonly used animal models in gastrointestinal alcohol research. We will also briefly discuss the findings based on animal models as well as the current concepts of pathophysiological mechanisms involved in acute and chronic alcoholic damage of the esophagus, stomach, small and large intestine, pancreas and liver.

Animal models in gastrointestinal alcohol research-a short appraisal of the different models and their results

Alcohol-related diseases of the gastrointestinal tract play an important role in clinical gastroenterology. However, the mechanisms and pathophysiology underlying the effects of ethanol on the organs of the digestive tract are not yet completely understood. Animal models represent an essential tool for investigating alcohol-related diseases because they give researchers the opportunity to use methods that cannot be used in humans, such as knockout technology. However, there is still a need for new animal models resembling the human condition, since for some alcohol-related diseases such as chronic alcoholic pancreatitis, the ideal animal model does not yet exist. In this chapter, we provide an overview of the most commonly used animal models in gastrointestinal alcohol research. We will also briefly discuss the current concepts of the pathophysiological mechanisms involved in acute and chronic alcoholic damage of the oesophagus, stomach, small and large intestine, pancreas and liver.

Local challenge of oral mucosa with gliadin in patients with coeliac disease

In coeliac disease, gluten-containing diet challenges over many years are sometimes required for diagnosis, especially if the initial diagnosis was equivocal. The rectal gluten challenge has been proposed to simplify coeliac disease diagnosis. We were interested in studying whether the oral mucosa could be used for local challenge with gliadin as an aid in finalizing the diagnosis of coeliac disease. The study groups consisted of 37 treated coeliac disease patients and 10 controls. The challenges on the oral mucosa were performed either supramucosally with gliadin powder (coeliac disease patients) or by submucosal injection of dissolved gliadin (10 microg/ml) (coeliac disease patients and controls). A control challenge with submucosal gliadin solvent was made in the coeliac disease patients. B and T cells, mast cells and T cell subsets were counted and HLA-DR expression was determined. Biopsies were taken from each provoked area 24 h post-challenge. A significant increase in the number of CD4+ lymphocytes in the lamina propria (observed in 27/37 patients), but a decrease in the number of mast cells was observed in treated coeliac disease patients after submucosal challenge with gliadin. Following supramucosal challenge with gliadin the counts of intraepithelial CD4+ (in 25/37 patients) and CD8+ T cells (in 27/37 patients) increased significantly and the number of CD4+ T cells in the lamina propria was also significantly increased. Control subjects were tested by submucosal gliadin challenge and no significant changes in the number of cells were observed. HLA-DR expression did not show increased positivity in coeliac disease patients on submucosal challenge. For the first time the oral mucosa has been used for immunological testing and shown to react to gliadin challenge in coeliac disease patients. Recruitment of T cells upon submucosal gliadin challenge occurred towards the lamina propria, whereas it occurred towards the epithelium in supramucosal gliadin challenge. The numbers of T cells increased in the lamina propria after submucosal challenge. The results suggest that local oral challenge with gliadin may be used as a diagnostic method in coeliac disease; however, further studies in untreated coeliac disease patients are needed to evaluate the usefulness of this method.

Osmotic changes and ethanol modify TFF gene expression in gastrointestinal cell lines

The gastrointestinal tract is exposed to environmental insult as a result of food intake or in pathological conditions such as diarrhoea, and is therefore protected by the mucus layer. As part of it, trefoil peptides (TFFs) are able to modify the visco-elastic properties of the mucus, protect against experimental ulceration, and promote repair of the epithelia. We investigated, using transient reporter gene assays and RT-PCR in the gastric carcinoma cell line MKN45 and colon carcinoma cell lines LS174T and HT29, whether ethanol and osmotic changes can modify transcriptional activity of TFFs. In a mild hypotonic environment (200 mosmol/l) all three TFF genes were up-regulated by at least a factor of 2. In hypertonic medium (400 mosmol/ll), TFF1 and TFF3 were down-regulated, whereas TFF2 was up-regulated by elevated concentrations of sodium or chloride in MKN45. Raising the osmolality by ethanol resulted in an up-regulation of TFF3 in both colon cell lines but not in the gastric cell line. We conclude that alteration in TFF gene expression is a response of gut epithelia to deal with osmotic forces and ethanol.