Defining NASH from a multi-omics systems biology perspective

Non-alcoholic steatohepatitis (NASH) is a chronic liver disease affecting up to 6.5% of the general population. There is no simple definition of NASH, and the molecular mechanism underlying disease pathogenesis remains elusive. Studies applying single omics technologies have enabled a better understanding of the molecular profiles associated with steatosis and hepatic inflammation—the commonly accepted histologic features for diagnosing NASH, as well as the discovery of novel candidate biomarkers. Multi-omics analysis holds great potential to uncover new insights into disease mechanism through integrating multiple layers of molecular information. Despite the technical and computational challenges associated with such efforts, a few pioneering studies have successfully applied multi-omics technologies to investigate NASH. Here, we review the most recent technological developments in mass spectrometry (MS)-based proteomics, metabolomics, and lipidomics. We summarize multi-omics studies and emerging omics biomarkers in NASH and highlight the biological insights gained through these integrated analyses

Inability of Some Commercial Assays to Measure Suppression of Glucagon Secretion

Glucagon levels are increasingly being included as endpoints in clinical study design and more than 400 current diabetes-related clinical trials have glucagon as an outcome measure. The reliability of immune-based technologies used to measure endogenous glucagon concentrations is, therefore, important. We studied the ability of immunoassays based on four different technologies to detect changes in levels of glucagon under conditions where glucagon levels are strongly suppressed. To our surprise, the most advanced technological methods, employing electrochemiluminescence or homogeneous time resolved fluorescence (HTRF) detection, were not capable of detecting the suppression induced by a glucose clamp (6 mmol/L) with or without atropine in five healthy male participants, whereas a radioimmunoassay and a spectrophotometry-based ELISA were. In summary, measurement of glucagon is challenging even when state-of-the-art immune-based technologies are used. Clinical researchers using glucagon as outcome measures may need to reconsider the validity of their chosen glucagon assay. The current study demonstrates that the most advanced approach is not necessarily the best when measuring a low-abundant peptide such as glucagon in humans

Glucagon Receptor Signaling and Glucagon Resistance

Hundred years after the discovery of glucagon, its biology remains enigmatic. Accurate measurement of glucagon has been essential for uncovering its pathological hypersecretion that underlies various metabolic diseases including not only diabetes and liver diseases but also cancers (glucagonomas). The suggested key role of glucagon in the development of diabetes has been termed the bihormonal hypothesis. However, studying tissue-specific knockout of the glucagon receptor has revealed that the physiological role of glucagon may extend beyond blood-glucose regulation. Decades ago, animal and human studies reported an important role of glucagon in amino acid metabolism through ureagenesis. Using modern technologies such as metabolomic profiling, knowledge about the effects of glucagon on amino acid metabolism has been expanded and the mechanisms involved further delineated. Glucagon receptor antagonists have indirectly put focus on glucagon’s potential role in lipid metabolism, as individuals treated with these antagonists showed dyslipidemia and increased hepatic fat. One emerging field in glucagon biology now seems to include the concept of hepatic glucagon resistance. Here, we discuss the roles of glucagon in glucose homeostasis, amino acid metabolism, and lipid metabolism and present speculations on the molecular pathways causing and associating with postulated hepatic glucagon resistance

Bile acids are important direct and indirect regulators of the secretion of appetite- and metabolism-regulating hormones from the gut and pancreas.

OBJECTIVE: Bile acids (BAs) facilitate fat absorption and may play a role in glucose and metabolism regulation, stimulating the secretion of gut hormones. The relative importance and mechanisms involved in BA-stimulated secretion of appetite and metabolism regulating hormones from the gut and pancreas is not well described and was the purpose of this study. METHODS: The effects of bile acids on the secretion of gut and pancreatic hormones was studied in rats and compared to the most well described nutritional secretagogue: glucose. The molecular mechanisms that underlie the secretion was studied by isolated perfused rat and mouse small intestine and pancreas preparations and supported by immunohistochemistry, expression analysis, and pharmacological studies. RESULTS: Bile acids robustly stimulate secretion of not only the incretin hormones, glucose-dependent insulinotropic peptide (GIP), and glucagon-like peptide-1 (GLP-1), but also glucagon and insulin in vivo, to levels comparable to those resulting from glucose stimulation. The mechanisms of GLP-1, neurotensin, and peptide YY (PYY) secretion was secondary to intestinal absorption and depended on activation of basolateral membrane Takeda G-protein receptor 5 (TGR5) receptors on the L-cells in the following order of potency: Lithocholic acid (LCA) >Deoxycholicacid (DCA)>Chenodeoxycholicacid (CDCA)> Cholic acid (CA). Thus BAs did not stimulate secretion of GLP-1 and PYY from perfused small intestine in TGR5 KO mice but stimulated robust responses in wild type littermates. TGR5 is not expressed on α-cells or β-cells, and BAs had no direct effects on glucagon or insulin secretion from the perfused pancreas. CONCLUSION: BAs should be considered not only as fat emulsifiers but also as important regulators of appetite- and metabolism-regulating hormones by activation of basolateral intestinal TGR5