Circulating Bile Acid Profiles: A Need for Further Examination

Bile acid and nonalcoholic steatohepatitis: Molecular insights and therapeutic targets

BACKGROUND

Nonalcoholic steatohepatitis (NASH) has been the second most common cause of liver transplantation in the United States. To date, NASH pathogenesis has not been fully elucidated but is multifactorial, involving insulin resistance, obesity, metabolic disorders, diet, dysbiosis, and gene polymorphism. An effective and approved therapy for NASH has also not been established. Bile acid is long known to have physiological detergent function in emulsifying and absorbing lipids and lipid-soluble molecules within the intestinal lumen. With more and more in-depth understandings of bile acid, it has been deemed to be a pivotal signaling molecule, which is capable of regulating lipid and glucose metabolism, liver inflammation, and fibrosis. In recent years, a plethora of studies have delineated that disrupted bile acid homeostasis is intimately correlated with NASH disease severity.

AIMS

The review aims to clarify the role of bile acid in hepatic lipid and glucose metabolism, liver inflammation, as well as liver fibrosis, and discusses the safety and efficacy of some pharmacological agents targeting bile acid and its associated pathways for NASH.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Bile acid has a salutary effect on hepatic metabolic disorders, which can ameliorate liver fat accumulation and insulin resistance mainly through activating Takeda G-protein coupled receptor 5 and farnesoid X receptor. Moreover, bile acid also exerts anti-inflammation and anti-fibrosis properties. Furthermore, bile acid has great potential in nonalcoholic liver disease stratification and treatment of NASH.

Understanding the gastrointestinal tract in obesity: From gut motility patterns to enzyme secretion

BACKGROUND AND PURPOSE

The pathophysiology of obesity has been the product of extensive research, revealing multiple interconnected mechanisms contributing to body weight regulation. The regulation of energy balance involves an intricate network, including the gut-neuroendocrine interplay. As a consequence, research on the gut-brain-microbiota axis in obesity has grown extensively. The physiology of the gastrointestinal tract, far from being underexplored, has significant implications for the development of specific complications in people living with obesity across the fields of gastroenterology, nutrition, and pharmacology. Clinical research indicates higher fasting bile acids serum levels, and blunted postprandial increases in bilious secretions in people living with obesity. Findings are less straightforward for the impact of obesity on gastric emptying with various studies reporting accelerated, normal, or delayed gastric emptying rates. Conversely, the effect of obesity on gastrointestinal pH, gastrointestinal transit, and gastric and pancreatic enzyme secretion is largely unknown. In this review, we explore the current evidence on the gastrointestinal physiology of obesity.

Predictive value of serum TBA for 2-year MACEs in ACS patients undergoing PCI: a prospective cohort study

Bile acids play important roles in lipid metabolism and glucose homeostasis. Limited research exist on the association between serum total bile acid (TBA) levels and major adverse cardiovascular events (MACEs) in patients with acute coronary syndrome (ACS), particularly those with comorbid type 2 diabetes mellitus (T2DM). This study was conducted to examine the relationship between baseline serum TBA level and T2DM status in patients with ACS after percutaneous coronary intervention (PCI) and to identify the predictive value of TBA levels for a 2-year risk of MACEs. 425 ACS patients underwent PCI were recruited and divided into three groups based on baseline serum TBA concentration. An analysis of the association between the T2DM status and baseline serum TBA levels was conducted using univariate linear regression and multivariate linear regression. The predictive relevance of serum TBA levels was evaluated using the receiver operating characteristic (ROC) curve and Cox regression. Kaplan-Meier curves were employed to analyze the differences among groups in predicting MACEs over a 2-year follow-up period. Baseline serum TBA levels were higher in ACS patients who were diagnosed with T2DM (the median 3.6 µmol/L) than those without T2DM (the median 3.0 µmol/L). T2DM status in ACS patients was positively correlated with baseline serum TBA concentrations (β: 1.7, 95% confidence interval [CI] 0.3-3.0), particularly in the male (β: 2.0, 95% CI 0.3-3.6) and 50-69-year-old (β: 2.5, 95% CI 0.6-4.4) populations. The areas under the ROC curve of baseline serum TBA levels predicted MACEs in ACS and ACS-T2DM patients following PCI were 0.649 (95% CI 0.595-0.703) and 0.783 (95% CI 0.685-0.881), respectively. Furthermore, Cox regression analysis showed that baseline serum TBA level was associated with the occurrence of MACEs in patients with ACS after PCI over a 2-year follow-up period, especially in those diagnosed with T2DM, whose baseline TBA concentration was lower than 10.0 µmol/L. ACS Patients with T2DM had higher serum TBA levels. TBA level at baseline was an independent predictor of MACEs in ACS patients who underwent PCI, especially with comorbid T2DM.

Obstructive Sleep Apnea, Circadian Clock Disruption, and Metabolic Consequences

Obstructive sleep apnea (OSA) is a chronic disorder characterized by recurrent episodes of apnea and hypopnea during sleep. It is associated with various cardiovascular and metabolic complications, including type 2 diabetes mellitus (T2DM) and obesity. Many pathways can be responsible for T2DM development in OSA patients, e.g., those related to HIF-1 and SIRT1 expression. Moreover, epigenetic mechanisms, such as miRNA181a or miRNA199, are postulated to play a pivotal role in this link. It has been proven that OSA increases the occurrence of circadian clock disruption, which is also a risk factor for metabolic disease development. Circadian clock disruption impairs the metabolism of glucose, lipids, and the secretion of bile acids. Therefore, OSA-induced circadian clock disruption may be a potential, complex, underlying pathway involved in developing and exacerbating metabolic diseases among OSA patients. The current paper summarizes the available information pertaining to the relationship between OSA and circadian clock disruption in the context of potential mechanisms leading to metabolic disorders.

Bile acid coordinates microbiota homeostasis and systemic immunometabolism in cardiometabolic diseases

Cardiometabolic disease (CMD), characterized with metabolic disorder triggered cardiovascular events, is a leading cause of death and disability. Metabolic disorders trigger chronic low-grade inflammation, and actually, a new concept of metaflammation has been proposed to define the state of metabolism connected with immunological adaptations. Amongst the continuously increased list of systemic metabolites in regulation of immune system, bile acids (BAs) represent a distinct class of metabolites implicated in the whole process of CMD development because of its multifaceted roles in shaping systemic immunometabolism. BAs can directly modulate the immune system by either boosting or inhibiting inflammatory responses via diverse mechanisms. Moreover, BAs are key determinants in maintaining the dynamic communication between the host and microbiota. Importantly, BAs via targeting Farnesoid X receptor (FXR) and diverse other nuclear receptors play key roles in regulating metabolic homeostasis of lipids, glucose, and amino acids. Moreover, BAs axis per se is susceptible to inflammatory and metabolic intervention, and thereby BAs axis may constitute a reciprocal regulatory loop in metaflammation. We thus propose that BAs axis represents a core coordinator in integrating systemic immunometabolism implicated in the process of CMD. We provide an updated summary and an intensive discussion about how BAs shape both the innate and adaptive immune system, and how BAs axis function as a core coordinator in integrating metabolic disorder to chronic inflammation in conditions of CMD.

Therapeutic effects and mechanism of liraglutide on rats with type 2 diabetes and metabolic-associated fatty liver disease

• Background SREBP-1c/Insig/SCAP acts as a lipid de novo synthesis pathway, and its factors are highly expressed in the endoplasmic reticulum[4]. At present, this pathway has become a research hotspot in the development of metabolic-associated fatty liver disease. However, there are few studies on how various factors in this pathway change after endoplasmic reticulum stress; in particular, the role of the insulin-inducing gene-1 (Insig-1) has not been elucidated in detail. • Objective To investigate whether liraglutide has a therapeutic effect on rats with T2DM and MAFLD and to further study its possible mechanism. • Method rats in the control group and modeling group were fed with normal diet and high-sugar and high-fat diet, respectively . After one month, the mice in the modeling group were injected with 35mg/kg STZ intraperitoneally to establish the model of type 2 diabetes mellitus. T2DM and MAFLD rats were randomly divided into three groups: model group, low dose liraglutide group, and high dose liraglutide group. Fasting blood glucose ,fasting insulin, blood lipid profile, alanine aminotransferase, and aspartate aminotransferase were measured at the end of the 8th week. Paraffin sections were obtained from the same part of the liver of rats in each group and observed by electron microscope after HE staining. Western blot was used to detect the expression of endoplasmic reticulum stress index (GRP78) and negative feedback index of lipid synthesis (Insig-1) in each group. • Results of Liver tissue from the drug intervention groups caused a decrease in lipid droplet vacuoles, and the hepatocytes were arranged neatly again. While the expression of GRP78 rose, Insig-1 declined. There were differences with different doses of liraglutide; the higher the dose was, the more obvious the effect. No such changes were observed in T2DM and MAFLD rats after injection of saline. • Conclusion, we show that liraglutide may have a therapeutic effect on rats with T2DM and MAFLD by reducing endoplasmic reticulum stress in the liver and increasing the expression of Insig-1.