Mechanism of gut-microbiota-liver axis in the pathogenesis of intestinal failure-associated liver disease / 中华胃肠外科杂志

Intestinal failure (IF) is defined as the critical reduction of functional intestines below the minimum needed to absorb nutrients and fluids, so that intravenous supplementation with parenteral nutrition (PN) is required to maintain health and/or growth. Although the benefits are evident, patients receiving PN can suffer from serious cholestasis due to lack of enteral feeding and small intestinal bacterial overgrowth (SIBO). One such complication that may arise is intestinal failure-associated liver disease (IFALD). Evidences from recent studies suggest that alterations in the intestinal microbiota, as well as intraluminal bile acid driven signaling, may play a critical role in both hepatic and intestinal injury. Since Marshall first proposed the concept of the gut-liver axis in 1998, the role of gut-liver axis disorders in the development of IFALD has received considerable attention. The conversation between gut and liver is the key to maintain liver metabolism and intestinal homeostasis, which influences each other and is reciprocal causation. However, as a "forgotten organ" , intestinal microbiota on the pathogenesis of IFALD has not been well reflected. As such, we propose, for the first time, the concept of gut-microbiota-liver axis to emphasize the importance of intestinal microbiota in the interaction of gut-liver axis. Analysis and research on gut-microbiota-liver axis will be of great significance for understanding the pathogenesis of IFALD and improving the prevention and treatment measures.

Bile Acid Diarrhea: Prevalence, Pathogenesis, and Therapy

Bile acid diarrhea (BAD) is usually seen in patients with ileal Crohn's disease or ileal resection. However, 25% to 50% of patients with functional diarrhea or diarrhea-predominant irritable bowel syndrome (IBS-D) also have evidence of BAD. It is estimated that 1% of the population may have BAD. The causes of BAD include a deficiency in fibroblast growth factor 19 (FGF-19), a hormone produced in enterocytes that regulates hepatic bile acid (BA) synthesis. Other potential causes include genetic variations that affect the proteins involved in BA enterohepatic circulation and synthesis or in the TGR5 receptor that mediates the actions of BA in colonic secretion and motility. BAs enhance mucosal permeability, induce water and electrolyte secretion, and accelerate colonic transit partly by stimulating propulsive high-amplitude colonic contractions. There is an increased proportion of primary BAs in the stool of patients with IBS-D, and some changes in the fecal microbiome have been described. There are several methods of diagnosing BAD, such as 75selenium homotaurocholic acid test retention, serum C4, FGF-19, and fecal BA measurement; presently, therapeutic trials with BA sequestrants are most commonly used for diagnosis. Management involves the use of BA sequestrants including cholestyramine, colestipol, and colesevelam. FXR agonists such as obeticholic acid constitute a promising new approach to treating BAD.

Evaluation of the Biodurability of Polyurethane-Covered Stent Using a Flow Phantom

OBJECTIVE:To evaluate the biodurability of the covering material in retrievable metallic stents covered with polycarbonate polyurethane. MATERIALS AND METHODS: Using a peristaltic pump at a constant rate of 1ml/min, bile was recirculated from a reservoir through a long tube containing four stents. Each of these was removed from the system every two weeks and a radial tensile strength test and scanning electron microscopy (SEM) were performed. Each stent, removed at 2, 4, 6 and 8 weeks, was compared with a control stent not exposed to bile juice. RESULTS: Gross examination showed that stents were intact at 2 weeks, but at 4, 6 and 8 weeks cracks were observed. The size of these increased gradually in accordance with the duration of exposure, and at 8 weeks several large holes in the polyurethane membrane were evident. With regard to radial tensile strength, extension and peak load at break were 84.47% and 10.030 N/mm, 54.90% and 6.769 N/mm, 16.55% and 2.452 N/mm, 11.21% and 1.373 N/mm at 0, 2, 4 and 6 weeks, respectively. Scanning electron microscopy at 2 weeks revealed intermittent pitting and cracking, and examination at 4, 6 and 8 weeks showed that the size of these defects was gradually increasing. CONCLUSION: When the polyurethane membrane was exposed to bile, biodegradation was first observed at week two and increased gradually according to the duration of exposure.

Mecanismos de defesa da bile / Defense mechanisms of the bile

Nesta revisao sao explicados cada um dos quatro mecanismos de defesa da bile contra a infecçao por microorganismos patógenos, bem como suas açoes integradas. Nesse contexto, incluem-se as barreiras anatômicas (complexos unitivos e esfíncter de Oddid), os mecanismos físicos (fluxo biliar e muco), os fatores químicos (sais biliares) e os mecanismos imunológicos (células de Kupffer e imunoglobulina A secretada). A quebra do funcionamento harmônico desses mecanismos pode levar a sérias infecçoes. Nesse sentido, o aumento da pressao intra-biliar (causada por obstruçao parcial ou completa do fluxo biliar) e doenças do parênquima hepático desempenham papel fundamental. Dessa forma, confirma-se a importância da preservaçao desses mecanismos de defesa no indivíduo saudável.

Fisiopatología de la litiasis biliar. Cálculos de colesterol

Biliary stones constitute an important issue in public health, until recently treated exclusively by surgical means. In the western world 80-90 percent of stones are composed of cholesterol, secondary to abnormalities in cholesterol and lipoprotein metabolism. In the last two decades significant advances in the treatment of this problem have been made, such as medical dissolution and extracorporeal lithotripsy. The most significant risk factors are: obesity, rapid weight loss, female sex, pregnancy, diabetes, hypertriglyceridemia, estrosalts derived from cholesterol are hydrophylic sterols that are essential to micelle formation. The predominance of the hydrophylic domain makes them amphophylic. Primary bile salts: cholate and deoxycholate are synthetized in the liver; secondary bile salts: deoxycholate and lithocholate derived from primary ones by bacterial transformation in the gut; tertiary bile salts: ursodeoxycholate and sulpholithocholate derived from secondary salts by bacterial action. Lecithin is the main phospholipid in bile, its main fuction is to solubilize cholesterol associated to bile salts. Micelles are complex structures made of cholesterol, lecithin and bile salts. Experimentally a triangular diagram has been designed representing molar concentrations of cholesterol, lecithin and bile salts. This diagram facilitates the understanding of biliary stones formation. Changing is components keeping constant total lipids, identifics several phases essential in stones formation, such as the micellar phase and the metastable phase. Supersaturated bile results from excess of cholesterol or deficiency of bile salts, and represents the initial abnormality that predispose to stones formation...