The biliary cycle of Moritz Schiff

The Hylemon-Björkhem pathway of bile acid 7-dehydroxylation: history, biochemistry, and microbiology

Bile acids are detergents derived from cholesterol that function to solubilize dietary lipids, remove cholesterol from the body, and act as nutrient signaling molecules in numerous tissues with functions in the liver and gut being the best understood. Studies in the early 20th century established the structures of bile acids, and by mid-century, the application of gnotobiology to bile acids allowed differentiation of host-derived "primary" bile acids from "secondary" bile acids generated by host-associated microbiota. In 1960, radiolabeling studies in rodent models led to determination of the stereochemistry of the bile acid 7-dehydration reaction. A two-step mechanism was proposed, which we have termed the Samuelsson-Bergström model, to explain the formation of deoxycholic acid. Subsequent studies with humans, rodents, and cell extracts of Clostridium scindens VPI 12708 led to the realization that bile acid 7-dehydroxylation is a result of a multi-step, bifurcating pathway that we have named the Hylemon-Björkhem pathway. Due to the importance of hydrophobic secondary bile acids and the increasing measurement of microbial bai genes encoding the enzymes that produce them in stool metagenome studies, it is important to understand their origin.

A history of research into the physiology of bile, from Hippocrates to molecular medicine

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Omega Loop Gastroileal Bypass (OLGIBP/SAGI) Versus One Anastomosis Gastric Bypass (OAGB): Medium-Term Results

INTRODUCTION

In bariatric surgery, new surgical techniques are continually being developed. The one anastomosis gastric bypass (OAGB) has become increasingly common since 2001. However, some patients experience bile reflux or excessive weight loss. This study aimed to assess a new bariatric procedure designed to avoid some of the drawbacks of conventional OAGB.

MATERIAL AND METHODS

To lower the complication rate and pathophysiological impact after OAGB, we performed an omega loop gastroileal bypass (OLGIBP/SAGI) with a 300-cm common limb. We compared this technique with OAGB.

RESULTS

Seventeen patients underwent OLGIBP and 23 underwent OAGB. Mean operative time was 108 min for OLGIBP vs 103 min for OAGB. The mean hospital length of stay was 3 days (1 to 7). No complications related to the gastroenterostomy occurred. At 3 years, among OAGB patients, there were 5 (21.7%) cases of bile reflux including 2 (8.7%) requiring a revision to Roux-en-Y gastric bypass. Among OLGIBP patients, there were 3 (17.6%) cases of bile reflux 1 (5.9%) requiring a revision to Roux-en-Y gastric bypass. There was no albumin deficiency. At 3 years, % of total weight loss (TWL) was 43.6 + - 6.2 in the OAGB group vs 48.2 + - 7.4 in the OLGIBP group.

CONCLUSIONS

The bariatric and metabolic outcomes of OLGIBP are expected to be similar to those of OAGB. The OLGIBP technique should reduce the risks of malnutrition and bile reflux. The two techniques can be safely performed and offer alternatives in bariatric surgery.

Bile Acid Receptor Therapeutics Effects on Chronic Liver Diseases

In the past ten years, our understanding of the importance of bile acids has expanded from fat absorption and glucose/lipid/energy homeostasis into potential therapeutic targets for amelioration of chronic cholestatic liver diseases. The discovery of important bile acid signaling mechanisms, as well as their role in metabolism, has increased the interest in bile acid/bile acid receptor research development. Bile acid levels and speciation are dysregulated during liver injury/damage resulting in cytotoxicity, inflammation, and fibrosis. An increasing focus to target bile acid receptors, responsible for bile acid synthesis and circulation, such as Farnesoid X receptor and apical sodium-dependent bile acid transporter to reduce bile acid synthesis have resulted in clinical trials for treatment of previously untreatable chronic liver diseases such as non-alcoholic steatohepatitis and primary sclerosing cholangitis. This review focuses on current bile acid receptor mediators and their effects on parenchymal and non-parenchymal cells. Attention will also be brought to the gut/liver axis during chronic liver damage and its treatment with bile acid receptor modulators. Overall, these studies lend evidence to the importance of bile acids and their receptors on liver disease establishment and progression.

Intestinal Absorption of Bile Acids in Health and Disease

The intestinal reclamation of bile acids is crucial for the maintenance of their enterohepatic circulation. The majority of bile acids are actively absorbed via specific transport proteins that are highly expressed in the distal ileum. The uptake of bile acids by intestinal epithelial cells modulates the activation of cytosolic and membrane receptors such as the farnesoid X receptor (FXR) and G protein-coupled bile acid receptor 1 (GPBAR1), which has a profound effect on hepatic synthesis of bile acids as well as glucose and lipid metabolism. Extensive research has focused on delineating the processes of bile acid absorption and determining the contribution of dysregulated ileal signaling in the development of intestinal and hepatic disorders. For example, a decrease in the levels of the bile acid-induced ileal hormone FGF15/19 is implicated in bile acid-induced diarrhea (BAD). Conversely, the increase in bile acid absorption with subsequent overload of bile acids could be involved in the pathophysiology of liver and metabolic disorders such as fatty liver diseases and type 2 diabetes mellitus. This review article will attempt to provide a comprehensive overview of the mechanisms involved in the intestinal handling of bile acids, the pathological implications of disrupted intestinal bile acid homeostasis, and the potential therapeutic targets for the treatment of bile acid-related disorders. Published 2020. Compr Physiol 10:21-56, 2020.

History of hepatic bile formation: old problems, new approaches

Studies of hepatic bile formation reported in 1958 established that it was an osmotically generated water flow. Intravenous infusion of sodium taurocholate established a high correlation between hepatic bile flow and bile acid excretion. Secretin, a hormone that stimulates bicarbonate secretion, was also found to increase hepatic bile flow. The sources of the water entering the biliary system with these two stimuli were differentiated by the use of mannitol. An increase in its excretion parallels the increase in bile flow in response to bile acids but not secretin, which led to a quantitative distinction between canalicular and ductular water flow. The finding of aquaglyceroporin-9 in the basolateral surface of the hepatocyte accounted for the rapid entry of mannitol into hepatocytes and its exclusion from water movement in the ductules where aquaporin-1 is present. Electron microscopy demonstrated that bile acids generate the formation of vesicles that contain lecithin and cholesterol after their receptor-mediated canalicular transport. Biophysical studies established that the osmotic effect of bile acids varies with their concentration and also with the proportion of mono-, di-, and trihydroxy bile acids and provides a basis for understanding their physiological effects. Because of the varying osmotic effect of bile acids, it is difficult to quantify bile acid independent flow generated by other solutes, such as glutathione, which enters the biliary system. Monohydroxy bile acids, by markedly increasing aggregation number, severely reduce water flow. Developing biomarkers for the noninvasive assessment of normal hepatic bile flow remains an elusive goal that merits further study.

Key discoveries in bile acid chemistry and biology and their clinical applications: history of the last eight decades

During the last 80 years there have been extraordinary advances in our knowledge of the chemistry and biology of bile acids. We present here a brief history of the major achievements as we perceive them. Bernal, a physicist, determined the X-ray structure of cholesterol crystals, and his data together with the vast chemical studies of Wieland and Windaus enabled the correct structure of the steroid nucleus to be deduced. Today, C24 and C27 bile acids together with C27 bile alcohols constitute most of the bile acid "family". Patterns of bile acid hydroxylation and conjugation are summarized. Bile acid measurement encompasses the techniques of GC, HPLC, and MS, as well as enzymatic, bioluminescent, and competitive binding methods. The enterohepatic circulation of bile acids results from vectorial transport of bile acids by the ileal enterocyte and hepatocyte; the key transporters have been cloned. Bile acids are amphipathic, self-associate in solution, and form mixed micelles with polar lipids, phosphatidylcholine in bile, and fatty acids in intestinal content during triglyceride digestion. The rise and decline of dissolution of cholesterol gallstones by the ingestion of 3,7-dihydroxy bile acids is chronicled. Scientists from throughout the world have contributed to these achievements.

Moritz schiff (1823-1896): a physiologist in exile

Moritz Schiff was one of the pioneers of modern experimental physiology. His involvement in the liberal movement forced him out of Germany, and, because of his adherence to proper physiological research, he had to flee Italy, his first refuge. The number and importance of his contributions are outstanding. The aim of this paper is to raise interest in his biography and to present a yet unreported field of research that is regarded as the root of functional imaging of the brain.

Telling the liver (not) to make bile acids: a new voice from the gut?

The maintenance of adequate amounts of bile acids in the liver, biliary tract, and intestine requires a finely tuned control of their synthesis. A paper in this issue of Cell Metabolism by Inagaki et al. (2005) indicates that sensing of the levels of bile acids in the intestine may trigger the secretion of a hormone which regulates bile acid production in the liver.