Bile acid sequestrants for lipid and glucose control

[Bile Acid Diarrhea]

Diarrhea is a very common gastrointestinal symptom, and the presence of higher concentrations of bile acid in the colon leads to bile acid diarrhea (BAD). In BAD patients, a portion of bile from the small intestine that is normally controlled by enterohepatic circulation is present at a high concentration in the lumen of the large intestine, resulting in increased motility and secretion of the large intestine. The prevalence of BAD is estimated to be 1-2% of the general population, and it comprises one-third of the instances of diarrhea-predominant irritable bowel syndrome. The clinical symptoms of BAD include chronic diarrhea, increased frequency of defecation, urgency to defecate, fecal incontinence, and cramping abdominal pain. The pathophysiology of BAD has not yet been fully elucidated. However, recent studies have reported increased intestinal permeability, shortened intestinal transit time, and changes in the intestinal microbial community to be the possible causes of BAD. Although fecal and serum bile acid tests are widely used for diagnosis, new test methods that are non-invasive, inexpensive, and have high sensitivity and specificity are needed at various institutions to facilitate the diagnosis. The selenium homo-tauro-cholic acid (SeHCAT) test is the gold standard for BAD diagnosis and severity assessment. The validation of several other serum markers, such as 7-hydroxy-4-cholesten-3-one (serum 7αC4) and the fibroblast growth factor 19 (FGF19) for use in clinical practice is ongoing. Although bile acid sequestrants are the mainstay of treatment, the development of drugs that are more effective and have better compliance is required. Farnesoid X receptor (FXR) agonists are showing promising results.

Research progress on the relationship between bile acid metabolism and type 2 diabetes mellitus

Bile acids, which are steroid molecules originating from cholesterol and synthesized in the liver, play a pivotal role in regulating glucose metabolism and maintaining energy balance. Upon release into the intestine alongside bile, they activate various nuclear and membrane receptors, influencing crucial processes. These bile acids have emerged as significant contributors to managing type 2 diabetes mellitus, a complex clinical syndrome primarily driven by insulin resistance. Bile acids substantially lower blood glucose levels through multiple pathways: BA-FXR-SHP, BA-FXR-FGFR15/19, BA-TGR5-GLP-1, and BA-TGR5-cAMP. They also impact blood glucose regulation by influencing intestinal flora, endoplasmic reticulum stress, and bitter taste receptors. Collectively, these regulatory mechanisms enhance insulin sensitivity, stimulate insulin secretion, and boost energy expenditure. This review aims to comprehensively explore the interplay between bile acid metabolism and T2DM, focusing on primary regulatory pathways. By examining the latest advancements in our understanding of these interactions, we aim to illuminate potential therapeutic strategies and identify areas for future research. Additionally, this review critically assesses current research limitations to contribute to the effective management of T2DM.

The German CaRe high registry for familial hypercholesterolemia - Sex differences, treatment strategies, and target value attainment

Background and aims

Familial hypercholesterolemia (FH) is among the most common genetic disorders in primary care. However, only 15% or less of patients are diagnosed, and few achieve the goals for low-density lipoprotein cholesterol (LDL-C). In this analysis of the German Cascade Screening and Registry for High Cholesterol (CaRe High), we examined the status of lipid management, treatment strategies, and LDL-C goal attainment according to the ESC/EAS dyslipidemia guidelines.

Methods

We evaluated consolidated datasets from 1501 FH patients diagnosed clinically and seen either by lipid specialists or general practitioners and internists. We conducted a questionnaire survey of both the recruiting physicians and patients.

Results

Among the 1501 patients, 86% regularly received lipid-lowering drugs. LDL-C goals were achieved by 26% and 10% of patients with atherosclerotic cardiovascular disease (ASCVD) according to the 2016 and 2019 ESC/EAS dyslipidemia guidelines, respectively. High intensity lipid-lowering was administered more often in men than in women, in patients with ASCVD, at higher LDL-C and in patients with a genetic diagnosis of FH.

Conclusions

FH is under-treated in Germany compared to guideline recommendations. Male gender, genetic proof of FH, treatment by a specialist, and presence of ASCVD appear to be associated with increased treatment intensity. Achieving the LDL-C goals of the 2019 ESC/EAS dyslipidemia guidelines remains challenging if pre-treatment LDL-C is very high.

Identification of Intestinal Microbial Community in Gallstone Patients with Metagenomic Next-Generation Sequencing

Gallstone disease (GD) is one of the most common gastrointestinal diseases worldwide. Nowadays, intestinal microbiota are thought to play important roles in the formation of gallstones. In our study, human fecal samples were extracted for metagenomic next-generation sequencing (mNGS) on the Illumina HiSeq platform, followed by bioinformatics analyses. Our results showed that there was a particular intestinal micro-ecosystem in GD patients. In contrast to healthy people, the sequences of Bacteroidetes, Bacteroides and Thetaiotaomicron were obviously more abundant in GD patients at phylum, genus and species levels, respectively. On the other hand, the glycan metabolism and drug resistance, especially for the β-lactams, were the most profound functions of gut microbes in GD patients compared to those in normal subjects. Furthermore, a correlation analysis drew out that there existed a significant relationship between the serum levels of biochemical indicators and abundances of intestinal microbes in GD patients. Our results illuminate both the composition and functions of intestinal microbiota in GD patients. All in all, our study can broaden the insight into the potential mechanism of how gut microbes affect the progression of gallstones to some extent, which may provide potential targets for the prevention, diagnosis or treatment of GD.

Bile Acid Sequestrants Based on Natural and Synthetic Gels

Bile acid sequestrants (BASs) are non-systemic therapeutic agents used for the management of hypercholesterolemia. They are generally safe and not associated with serious systemic adverse effects. Usually, BASs are cationic polymeric gels that have the ability to bind bile salts in the small intestine and eliminate them by excretion of the non-absorbable polymer-bile salt complex. This review gives a general presentation of bile acids and the characteristics and mechanisms of action of BASs. The chemical structures and methods of synthesis are shown for commercial BASs of first- (cholestyramine, colextran, and colestipol) and second-generation (colesevelam and colestilan) and potential BASs. The latter are based on either synthetic polymers such as poly((meth)acrylates/acrylamides), poly(alkylamines), poly(allylamines) and vinyl benzyl amino polymers or biopolymers, such as cellulose, dextran, pullulan, methylan, and poly(cyclodextrins). A separate section is dedicated to molecular imprinting polymers (MIPs) because of their great selectivity and affinity for the template molecules used in the imprinting technique. Focus is given to the understanding of the relationships between the chemical structure of these cross-linked polymers and their potential to bind bile salts. The synthetic pathways used in obtaining BASs and their in vitro and in vivo hypolipidemic activities are also introduced.

Gut microbiota: A new target for traditional Chinese medicine in the treatment of depression

ETHNIC PHARMACOLOGICAL RELEVANCE

The causes of depression are complex. Many factors are involved in its pathogenesis, including the individual's biological and social environment. Although numerous studies have reported that the gut microbiota plays a significant role in depression, drugs that regulate the gut microbiota to treat depression have not yet been comprehensively reviewed. At the same time, more and more attention has been paid to the characteristics of traditional Chinese medicine (TCM) in improving depression by regulating gut microbiota. In ancient times, fecal microbiota transplantation was recorded in TCM for the treatment of severe diseases. There are also records in Chinese ancient books about the use of TCM to adjust gut microbiota to treat diseases, which has opened up a unique research field in TCM. Therefore, this article focuses on the pharmacological effects, targets, and mechanisms of TCM in improving depression by mediating the influence of gut microbiota.

AIM OF THIS REVIEW

To summarize the role the gut microbiota plays in depression, highlight potential regulatory targets, and elucidate the anti-depression mechanisms of TCMs through regulation of the gut microbiota.

METHODS

A systematic review of 256 clinical trials and pharmaceutical studies published until June 2022 was conducted in eight electronic databases (Web of Science, PubMed, SciFinder, Research Gate, ScienceDirect, Google Scholar, Scopus, and China Knowledge Infrastructure), according to the implemented PRISMA criteria, using the search terms "traditional Chinese medicine," "depression," and "gut microbiota."

RESULTS

Numerous studies reported the effects of different gut bacteria on depression and that antidepressants work through the gut microbiota. TCM preparations based on compound Chinese medicine, the Chinese Materia Medica, and major bioactive components exerted antidepressant-like effects by improving levels of neurotransmitters, short-chain fatty acids, brain-derived neurotrophic factor, kynurenine, and cytokines via regulation of the gut microbiota.

CONCLUSION

This review summarized the anti-depression effects of TCM on the gut microbiota, providing evidence that TCMs are safe and effective in the treatment of depression and may provide a new therapeutic approach.

Biological tuners to reshape the bile acid pool for therapeutic purposes in non-alcoholic fatty liver disease

Bile acids synthesized within the hepatocytes are transformed by gut microorganisms and reabsorbed into the portal circulation. During their enterohepatic cycling, bile acids act as signaling molecules by interacting with receptors to regulate pathways involved in many physiological processes. The bile acid pool, composed of a variety of bile acid species, has been shown to be altered in diseases, hence contributing to disease pathogenesis. Thus, understanding the changes in bile acid pool size and composition in pathological processes will help to elaborate effective pharmacological treatments. Five crucial steps along the enterohepatic cycle shape the bile acid pool size and composition, offering five possible targets for therapeutic intervention. In this review, we provide an insight on the strategies to modulate the bile acid pool, and then we discuss the potential benefits in non-alcoholic fatty liver disease.

Untargeted Metabolomics Reveals the Function of GPRC6A in Amino Acid and Lipid Metabolism in Mice

GPRC6A is an amino acid sensor in the cytomembrane. Despite substantial evidence for the role of GPRC6A in metabolism, the specific effects and mechanism by which this gene acts on metabolic processes are still unresolved. In this study, serum biochemical parameters related to liver and kidney function and serum amino acid levels were determined in GPRC6A wild-type (WT) and knockout (KO) mice. An untargeted serum metabolomics analysis was also conducted for the first time, to the best of our knowledge, to decipher the function of GPRC6A in metabolic processes. GPRC6A was involved in lipid and amino acid metabolism, mainly by affecting liver function. A loss of GPRC6A function may perturb bile acid metabolism, thus leading to abnormal unsaturated fatty acid metabolism. GPRC6A KO may lead to excessive protein breakdown under starvation, and the loss of GPRC6A had a significant effect on phenylalanine metabolism-related pathways. Our metabolomics data provide a novel basis for further functional studies of GPRC6A.

Investigation of dysregulated lipid metabolism in diabetic mice via targeted metabolomics of bile acids in enterohepatic circulation

RATIONALE

The mechanism of lipid metabolism disorder in type 2 diabetes (T2DM) remains unclear. This study aimed to reveal the mechanism underlying dysregulated lipid metabolism in T2DM through bile acid metabolism.

METHODS

A db/db mouse model was employed to investigate the alteration of bile acid profiles in T2DM. Ultrahigh-performance liquid chromatography with tandem mass spectrometry was used to quantify the detailed bile acid levels in each compartment of enterohepatic circulation. The pathological change of mouse liver was assessed by liver histology and serum biochemical assays. The expression level of bile acid-related transporters and synthases was measured with Western blot analysis.

RESULTS

The results showed that T2DM can result in severe liver fat accumulation and liver damage. In addition, compared to the control group, in T2DM mice, bile acid synthesis is reduced, while the level of bile acids is increased at the storage sites and the reabsorption sites, but there are subtle gender differences. Further, the ratio of conjugated bile acids in total bile acid in the liver of T2DM mice increased significantly relative to the control group for both female and male mice.

CONCLUSIONS

In T2DM, bile acid metabolism is disordered in both male and female mice, which could be the underlying mechanism of dysregulated lipid metabolism in T2DM.

Bile Acid Sequestrants for Hypercholesterolemia Treatment Using Sustainable Biopolymers: Recent Advances and Future Perspectives

Bile acids, the endogenous steroid nucleus containing signaling molecules, are responsible for the regulation of multiple metabolic processes, including lipoprotein and glucose metabolism to maintain homeostasis. Within our body, they are directly produced from their immediate precursors, cholesterol C (low-density lipoprotein C, LDL-C), through the enzymatic catabolic process mediated by 7-α-hydroxylase (CYP7A1). Bile acid sequestrants (BASs) or amphiphilic resins that are nonabsorbable to the human body (being complex high molecular weight polymers/electrolytes) are one of the classes of drugs used to treat hypercholesterolemia (a high plasma cholesterol level) or dyslipidemia (lipid abnormalities in the body); thus, they have been used clinically for more than 50 years with strong safety profiles as demonstrated by the Lipid Research Council-Cardiovascular Primary Prevention Trial (LRC-CPPT). They reduce plasma LDL-C and can slightly increase high-density lipoprotein C (HDL-C) levels, whereas many of the recent clinical studies have demonstrated that they can reduce glucose levels in patients with type 2 diabetes mellitus (T2DM). However, due to higher daily dosage requirements, lower efficacy in LDL-C reduction, and concomitant drug malabsorption, research to develop an "ideal" BAS from sustainable or natural sources with better LDL-C lowering efficacy and glucose regulations and lower side effects is being pursued. This Review discusses some recent developments and their corresponding efficacies as bile removal or LDL-C reduction of natural biopolymer (polysaccharide)-based compounds.

Role of FXR in Bile Acid and Metabolic Homeostasis in NASH: Pathogenetic Concepts and Therapeutic Opportunities

Nonalcoholic fatty liver disease (NAFLD) has become the most prevalent cause of liver disease, increasingly contributing to the burden of liver transplantation. In search for effective treatments, novel strategies addressing metabolic dysregulation, inflammation, and fibrosis are continuously emerging. Disturbed bile acid (BA) homeostasis and microcholestasis via hepatocellular retention of potentially toxic BAs may be an underappreciated factor in the pathogenesis of NAFLD and nonalcoholic steatohepatitis (NASH) as its progressive variant. In addition to their detergent properties, BAs act as signaling molecules regulating cellular homeostasis through interaction with BA receptors such as the Farnesoid X receptor (FXR). Apart from being a key regulator of BA metabolism and enterohepatic circulation, FXR regulates metabolic homeostasis and has immune-modulatory effects, making it an attractive therapeutic target in NAFLD/NASH. In this review, the molecular basis and therapeutic potential of targeting FXR with a specific focus on restoring BA and metabolic homeostasis in NASH is summarized.

The Gut Microbiome: Connecting Diet, Glucose Homeostasis, and Disease

Type 2 diabetes rates continue to rise unabated, underscoring the need to better understand the etiology and potential therapeutic options available for this disease. The gut microbiome plays a role in glucose homeostasis, and diabetes is associated with alterations in the gut microbiome. Given that consumption of a Western diet is associated with increased metabolic disease, and that a Western diet alters the gut microbiome, it is plausible that changes in the gut microbiota mediate the dysregulation in glucose homeostasis. In this review, we highlight a few of the most significant mechanisms by which the gut microbiome can influence glucose regulation, including changes in gut permeability, gut-brain signaling, and production of bacteria-derived metabolites like short-chain fatty acids and bile acids. A better understanding of these pathways could lead to the development of novel therapeutics to target the gut microbiome in order to restore glucose homeostasis in metabolic disease. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Dyslipidemia Management in 2020: An Update on Diagnosis and Therapeutic Perspectives

Cardiovascular diseases are the leading cause of death in the modern world and dyslipidemia is one of the major risk factors. The current therapeutic strategies for cardiovascular diseases involve the management of risk factors, especially dyslipidemia and hypertension. Recently, the updated guidelines of dyslipidemia management were presented, and the newest data were included in terms of diagnosis, imaging, and treatment. In this targeted literature review, the researchers presented the most recent evidence on dyslipidemia management by including the current therapeutic goals for it. In addition, the novel diagnostic tools based on theranostics are shown. Finally, the future perspectives on treatment based on novel drug delivery systems and their potential to be used in clinical trials were also analyzed. It should be noted that dyslipidemia management can be achieved by the strict lifestyle change, i.e., by adopting a healthy life, and choosing the most suitable medication. This review can help medical professionals as well as specialists of other sciences to update their knowledge on dyslipidemia management, which can lead to better therapeutic outcomes and newer drug developments.

Bile acid diarrhoea: Current and potential methods of diagnosis

Chronic diarrhoea is common and mostly due to diarrhoea predominant irritable bowel syndrome. Diarrhoea predominant irritable bowel syndrome affects about 11% of the population; however, up to a third of these patients actually have bile acid diarrhoea. There are, therefore, more than one million sufferers of bile acid diarrhoea in the UK. Bile acid diarrhoea is caused by small bowel malabsorption of bile acids and the increased bile acids in the large intestine cause diarrhoea. Once diagnosed, the treatment of bile acid diarrhoea is simple and effective. Bile acid diarrhoea , however, is often not diagnosed because of a lack of easily available and reliable diagnostic methods. In the United Kingdom, the radiolabelled 23-seleno-25-homotaurocholic acid test is the gold-standard method of diagnosis. 23-seleno-25-homotaurocholic acid test, however, is expensive, inconvenient to the patient, involves radiation exposure and has limited availability. As such, a laboratory biomarker is desirable. This review briefly discusses the pathophysiology and management of bile acid diarrhoea and critically evaluates methods for its diagnosis, including serum 7α-hydroxy-4-cholesten-3-one, faecal bile acid measurement, serum fibroblast growth factor 19, urine-2-propanol, and the ¹⁴C-glycocholate breath and stool test.

Proceedings of the 2017 ASPEN Research Workshop-Gastric Bypass: Role of the Gut

The goal of the National Institutes of Health-funded American Society for Parenteral and Enteral Nutrition 2017 research workshop (RW) "Gastric Bypass: Role of the Gut" was to focus on the exciting research evaluating gut-derived signals in modulating outcomes after bariatric surgery. Although gastric bypass surgery has undoubted positive effects, the mechanistic basis of improved outcomes cannot be solely explained by caloric restriction. Emerging data suggest that bile acid metabolic pathways, luminal contents, energy balance, gut mucosal integrity, as well as the gut microbiota are significantly modulated after bariatric surgery and may be responsible for the variable outcomes, each of which was rigorously evaluated. The RW served as a timely and novel academic meeting that brought together clinicians and researchers across the scientific spectrum, fostering a unique venue for interdisciplinary collaboration among investigators. It promoted engaging discussion and evolution of new research hypotheses and ideas, driving the development of novel ameliorative, therapeutic, and nonsurgical interventions targeting obesity and its comorbidities. Importantly, a critical evaluation of the current knowledge regarding gut-modulated signaling after bariatric surgery, potential pitfalls, and lacunae were thoroughly addressed.

Bile acids in glucose metabolism and insulin signalling - mechanisms and research needs

Of all the novel glucoregulatory molecules discovered in the past 20 years, bile acids (BAs) are notable for the fact that they were hiding in plain sight. BAs were well known for their requirement in dietary lipid absorption and biliary cholesterol secretion, due to their micelle-forming properties. However, it was not until 1999 that BAs were discovered to be endogenous ligands for the nuclear receptor FXR. Since that time, BAs have been shown to act through multiple receptors (PXR, VDR, TGR5 and S1PR2), as well as to have receptor-independent mechanisms (membrane dynamics, allosteric modulation of N-acyl phosphatidylethanolamine phospholipase D). We now also have an appreciation of the range of physiological, pathophysiological and therapeutic conditions in which endogenous BAs are altered, raising the possibility that BAs contribute to the effects of these conditions on glycaemia. In this Review, we highlight the mechanisms by which BAs regulate glucose homeostasis and the settings in which endogenous BAs are altered, and provide suggestions for future research.

Drug repurposing in alternative medicine: herbal digestive Sochehwan exerts multifaceted effects against metabolic syndrome

New drug development is a challenging process that requires high-risk, huge costs and long lead times. Therefore, drug repurposing is considered a strategic and economic way towards successful drug development. Sochehwan (SCH) is a herbal formula well known as a digestive aid in traditional oriental medicine, is referred to in classic medical texts, and is available as an over-the-counter drug for indications of digestive ailments. Interestingly, another medical text written in earlier age describes different indication of SCH yet to be examined. We conducted a series of investigations using maturated adipocytes, free fatty acid (FFA) induced hepatic steatosis model in vitro and high-fat diet (HFD) mice model in vivo. Exposure to SCH regulated expression of adipogenic genes and proteins, significantly inhibiting formation of lipid droplets in 3T3-L1 cells. Similarly, SCH treatment modulated proteins related with energy metabolism decreasing lipid accumulation in FFA induced HepG2 cells. Furthermore, HFD-fed c57BL/6 J mice supplemented with SCH exhibited significant changes in serum glucose and lipid profiles. Histologic analysis of mice liver and adipose tissue showed that SCH administration attenuated hepatic steatosis and hypertrophy of adipose tissue. In overall, the results show that SCH can potentially be used to treat metabolic syndrome (MetS) by enhancing glucose metabolism and inhibiting lipogenesis through activating AMP-activated protein kinase (AMPK) and its downstream signaling. Furthermore, it seems to be a feasible drug repurposing strategy for drugs originating from alternative medicine to revise the value for buried indications of some herbal prescription in old traditional Chinese Medicine (TCM) classics.

Bile acids and the metabolic syndrome

Bile acids have important roles in the regulation of lipid, glucose and energy metabolism. Metabolic diseases linked to obesity, including type 2 diabetes mellitus and non-alcoholic fatty liver disease, are associated with dysregulation of bile acid homeostasis. Here, the basic chemistry and regulation of bile acids as well as their metabolic effects will be reviewed. Changes in circulating bile acids associated with obesity and related diseases will be reviewed. Finally, pharmaceutical manipulation of bile acid homeostasis as therapy for metabolic diseases will be outlined.

Abnormality of intestinal cholesterol absorption in ApcMin/+ mice with colon cancer cachexia

Colorectal cancer syndrome has been one of the greatest concerns in the world, particularly in developed countries. Several epidemiological studies have shown that dyslipidemia may be associated with the progression of intestinal cachexia, but there is little research on the function of the small intestine, which is involved in blood lipid metabolism, in dyslipidemia. In the present study, we aimed to explore the function of intestinal cholesterol absorption in the Apc^Min/+ mouse model using an intestinal lipid absorption test. We found that both triglyceride (TG) and total cholesterol (TC) uptake were inhibited in the intestine of Apc^Min/+ mice with age and the intestinal peroxisome proliferator-activated receptor α (PPARα) downregulated the processes of β-oxidation, oxidative stress response, and cholesterol absorption in APC-deficient mice. In addition, reduced expression levels of farnesoid X receptor (FXR) and apical sodium-dependent bile acid transporter (ASBT) indicated that bile acid metabolism might be associated with intestinal cholesterol absorption in Apc^Min/+ mice. Thus, our data suggested that the intestine plays an essential role in cholesterol uptake and that bile acid metabolism seems to cause a decrease in intestinal cholesterol uptake in Apc^Min/+ mice.

Potential Applications of Gliclazide in Treating Type 1 Diabetes Mellitus: Formulation with Bile Acids and Probiotics

A major advancement in therapy of type 1 diabetes mellitus (T1DM) is the discovery of new treatment which avoids and even replaces the absolute requirement for injected insulin. The need for multiple drug therapy of comorbidities associated with T1DM increases demand for developing novel therapeutic alternatives with new mechanisms of actions. Compared to other sulphonylurea drugs used in the treatment of type 2 diabetes mellitus, gliclazide exhibits a pleiotropic action outside pancreatic β cells, the so-called extrapancreatic effects, such as antiinflammatory and cellular protective effects, which might be beneficial in the treatment of T1DM. Results from in vivo experiments confirmed the positive effects of gliclazide in T1DM that are even more pronounced when combined with other hypoglycaemic agents such as probiotics and bile acids. Even though the exact mechanism of interaction at the molecular level is still unknown, there is a clear synergistic effect between gliclazide, bile acids and probiotics illustrated by the reduction of blood glucose levels and improvement of diabetic complications. Therefore, the manipulation of bile acid pool and intestinal microbiota composition in combination with old drug gliclazide could be a novel therapeutic approach for patients with T1DM.

Insulin Action Research and the Future of Diabetes Treatment: The 2017 Banting Medal for Scientific Achievement Lecture

Diabetes is caused by combined abnormalities in insulin production and action. The pathophysiology of these defects has been studied extensively and is reasonably well understood. Their causes are elusive and their manifestations pleiotropic, likely reflecting the triple threat of genes, environment, and lifestyle. Treatment, once restricted to monotherapy with secretagogues or insulin, now involves complex combinations of expensive regimens that stem the progression but do not fundamentally alter the underlying causes of the disease. As advances in our understanding of insulin action and β-cell failure reach a critical stage, here I draw on lessons learned from our research on insulin regulation of gene expression and pancreatic β-cell dedifferentiation to address the question of how we can translate this exciting biology into mechanism-based interventions to reverse the course of diabetes.

Insulin resistance and vascular dysfunction in chronic kidney disease: mechanisms and therapeutic interventions

Insulin resistance (IR) is a novel cardiovascular risk factor that has been implicated in the pathogenesis of cardiovascular disease (CVD) in patients with chronic kidney disease (CKD). Beyond its metabolic effects, insulin can potentially mediate the increased risk for CVD through its vasoactive properties. This review examines key clinical data and potential mechanisms linking IR and cardiovascular risk in CKD. While lifestyle interventions and pharmacotherapies with known insulin-sensitizing properties are promising therapeutic targets to reduce the CVD burden in this population, clinical trial data on the effect of insulin sensitization on vascular function in CKD are either lacking or conflicting and are limited by small sample size and short duration of intervention. Affirming the role of IR in lowering CVD risk in CKD will require prospective randomized controlled studies with sufficient sample size and hard clinical outcomes. Future research efforts should be directed at assessing the efficacy, safety and mechanisms by which novel insulin sensitizers such as bile acid sequestrant, selective and dual peroxisome proliferator-activated receptor modulators and modulators of gut microbiota and uraemic toxins alter vascular function in patients with CKD.

Diet1, bile acid diarrhea, and FGF15/19: mouse model and human genetic variants

Diet1 modulates intestinal production of the hormone, fibroblast growth factor (FGF)15, which signals in liver to regulate bile acid synthesis. C57BL/6ByJ mice with a spontaneous Diet1-null mutation are resistant to hypercholesterolemia compared with wild-type C57BL/6J mice through enhanced cholesterol conversion to bile acids. To further characterize the role of Diet1 in metabolism, we generated Diet1^-/- mice on the C57BL/6J genetic background. C57BL/6J Diet1^-/- mice had elevated bile acid levels, reduced Fgf15 expression, and increased gastrointestinal motility and intestinal luminal water content, which are symptoms of bile acid diarrhea (BAD) in humans. Natural genetic variation in Diet1 mRNA expression levels across 76 inbred mouse strains correlated positively with Ffg15 mRNA and negatively with serum bile acid levels. This led us to investigate the role of DIET1 genetic variation in primary BAD patients. We identified a DIET1 coding variant (rs12256835) that had skewed prevalence between BAD cases and controls. This variant causes an H1721Q amino acid substitution that increases the levels of FGF19 protein secreted from cultured cells. We propose that genetic variation in DIET1 may be a determinant of FGF19 secretion levels, and may affect bile acid metabolism in both physiological and pathological conditions.

Early Combination Therapy with Oral Glucose-Lowering Agents in Type 2 Diabetes

Despite the considerable burden of disease associated with type 2 diabetes mellitus (T2DM), most patients are not at, or are unable to achieve, recommended glycemic targets. This is partly because of the relentless progressive nature of the disease, but it may also be attributable to the current diabetes treatment paradigm. The recommended stepwise approach may lead to frequent early treatment failure with prolonged periods of elevated glucose as a consequence of clinical inertia and delays in achieving optimal glycemic control. Thus, it is most appropriate to consider the current treatment paradigm for T2DM in the context of a more aggressive initial therapy with early combination therapy. Current guidelines advise that initial combination therapy should be used for patients presenting with elevated glycated hemoglobin (HbA_1c). However, several studies and recent meta-analyses suggest a potential benefit from initial combination therapy on glycemic outcomes in diabetes compared with metformin monotherapy across a wide range of baseline HbA_1c levels. Indeed, combination therapy can increase the number of patients achieving glycemic goals, and the newer glucose-lowering agents may reduce the risk of hypoglycemia and body weight gain. Moreover, our improving understanding of the complex pathophysiology of T2DM and the availability of treatments tackling specific mechanisms contributing to hyperglycemia should lead to more pathophysiologically sound combination therapy. We discuss the rationale behind and evidence for early combination therapy as well as what is needed in the future to better understand its potential.

Sevelamer Improves Steatohepatitis, Inhibits Liver and Intestinal Farnesoid X Receptor (FXR), and Reverses Innate Immune Dysregulation in a Mouse Model of Non-alcoholic Fatty Liver Disease

Bile acid sequestrants are synthetic polymers that bind bile acids in the gut and are used to treat dyslipidemia and hyperphosphatemia. Recently, these agents have been reported to lower blood glucose and increase insulin sensitivity by altering bile acid signaling pathways. In this study, we assessed the efficacy of sevelamer in treating mice with non-alcoholic fatty liver disease (NAFLD). We also analyzed how sevelamer alters inflammation and bile acid signaling in NAFLD livers. Mice were fed a low-fat or Western diet for 12 weeks followed by a diet-plus-sevelamer regimen for 2 or 12 weeks. At the end of treatment, disease severity was assessed, hepatic leukocyte populations were examined, and expression of genes involved in farnesoid X receptor (FXR) signaling in the liver and intestine was analyzed. Sevelamer treatment significantly reduced liver steatosis and lobular inflammation. Sevelamer-treated NAFLD livers had notably fewer pro-inflammatory infiltrating macrophages and a significantly greater fraction of alternatively activated Kupffer cells compared with controls. Expression of genes involved in FXR signaling in the liver and intestine was significantly altered in mice with NAFLD as well as in those treated with sevelamer. In a mouse model of NAFLD, sevelamer improved disease and counteracted innate immune cell dysregulation in the liver. This study also revealed a dysregulation of FXR signaling in the liver and intestine of NAFLD mice that was counteracted by sevelamer treatment.

Spirogyra neglecta inhibits the absorption and synthesis of cholesterol in vitro

Background

Spirogyra neglecta (SN) has many nutritional benefits and it is commonly used to ameliorate different human conditions including inflammation, gastric ulcer, hyperglycemia, and hyperlipidemia. However, the mechanism of the hypocholesterolemic effect of SN still remains unclear. Therefore, the present study was aimed to evaluate the effect of SN extract particularly on cholesterol absorption and synthesis mechanisms.

Methods

For cholesterol absorption, the uptake of cholesterol was measured by using tritium radiolabeling of cholesterol in Caco-2 cells. Bile acid binding, micelles size, and cholesterol solubility were analyzed in in vitro assays, while cholesterol synthesis was evaluated by using a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase assay kit.

Results

SN extract was found to decrease cholesterol uptake in Caco-2 cells and decreased the solubility of cholesterol in micelles. The SN extract bound to taurocholate, taurodeoxycholate, and glycodeoxycholate bile acids, and increased micelles size. SN has also demonstrated an inhibitory effect on HMG-CoA reductase (HMGR) enzymatic activity. For further experimentation, the treatment combination of SN and ezetimibe (0.04 mg/mL) showed a greater significant reduction in cholesterol uptake than the extract alone.

Conclusion

These observations suggested that inhibitory cholesterol absorption effects of SN could be mediated through the modulation of size and solubility of cholesterol micelles, resulting in interference of cholesterol uptake. In addition, SN inhibited the rate limiting step of cholesterol synthesis. This study provides supporting evidence for the potential usage of SN as a cholesterol lowering agent.

Perspectives on Treatment for Nonalcoholic Steatohepatitis

It is important to provide treatment to patients with nonalcoholic steatohepatitis (NASH) because one third of patients with the metabolic syndrome die of liver disease. Basic research studies have elucidated mechanisms of NASH pathogenesis, which could lead to therapeutic targets. Health agencies have confirmed strategies for the optimal management of NASH and approved new drugs and treatments, which urgently are needed. The US Food and Drug Administration recently endorsed end points for NASH therapy. The reversal of NASH with no evidence of progression to advanced fibrosis has been defined as the end point for phase 2b and phase 3 trials in patients with NASH and early stage fibrosis. Although a decrease in the nonalcoholic fatty liver disease activity score could serve as an end point in clinical trials, it is not clear whether patients with lower scores have a lower risk of progression to advanced fibrosis. End points for clinical trials of patients with NASH cirrhosis currently are based on model for end-stage liver disease and Child-Pugh-Turcotte scores, as well as the hepatic venous pressure gradient. Different strategies are being explored to reduce liver diseases that are linked to a sedentary lifestyle, overeating, and genetic factors. In association with insulin resistance and deregulation of the lipid metabolism (accumulation of lipotoxins that promote hepatic lipogenesis, adipose tissue lipolysis, and impaired β-oxidation), these factors could increase the risk of liver steatosis with necroinflammatory lesions and fibrosis. We review the pathogenic mechanisms of NASH and therapeutic options, as well as strategies that are being developed for the treatment of injury to the liver and other organs.

Current drug treatment of hyperlipidemia in older adults

Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of death, especially in older adults. Managing modifiable risk factors (e.g., hyperlipidemia, hypertension) remains the primary approach to prevent ASCVD events and ASCVD-related mortality. Statins are generally considered one of the most effective approaches to reduce ASCVD risk, especially for secondary prevention, yet remain underutilized in older adults. The evidence to support statin therapy in older adults is less robust than in their younger counterparts, especially in individuals aged 75 years and older. Recent lipid guidelines have raised this concern, yet statin therapy is recommended in 'at risk' older adults. Determining which older adults should receive statin therapy for primary prevention of ASCVD is challenging, as the currently available risk estimation tools are of limited use in those aged over 75 years. Furthermore, non-statin therapies have been de-emphasized in recent clinical practice guidelines and remain understudied in the older adult population. This is unfortunate given that older adults are less likely to tolerate moderate- to high-intensity statins. Non-statin therapies could be viable options in this population if more was understood about their ability to lower ASCVD risk and safety profiles. Nevertheless, lipid-lowering agents remain an integral component of the overall strategy to reduce atherogenic burden in older adults. Future research in this area should aim to enroll more older adults in clinical trials, determine the utility of ASCVD risk estimation for primary prevention, and investigate the role of non-statin therapies in this population.

Bile Acid Metabolome after an Oral Lipid Tolerance Test by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Context

Besides their role in intestinal resorption of lipids, bile acids are regarded as endocrine and metabolic signaling molecules. The detailed profile of bile acid species in peripheral blood after an oral lipid tolerance test (OLTT) is unknown.

Objective

We quantified the regulation of 18 bile acids after OLTT in healthy individuals.

Material and methods

100 volunteers were characterized by anthropometric and laboratory parameters and underwent OLTT. Venous blood was drawn in the fasted state (0 h) and at 2h, 4h, and 6 h after OLTT. Serum concentrations of 18 bile acids were measured by LC-MS/MS.

Results

All of the 6 taurine-conjugated bile acids (TUDCA, THDCA, TCA, TCDCA, TDCA, TLCA) and all of the 6 glycine-conjugated bile acids (GUDCA, GHDCA, GCA, GCDCA, GDCA, GLCA) rose significantly at 2h and remained elevated during OLTT. Of the primary bile acids, CA remained unchanged, whereas CDCA significantly decreased at 4h. Of the secondary bile acids, DCA, UDCA and HDCA were not altered, whereas LCA decreased. There was a significant positive correlation between the intestinal feed-back regulator of bile acid synthesis FGF-19 and bile acids. This correlation seems to depend on all of the six taurine-conjugated bile acids and on GCA, GDCA, and GCDCA. Females and users of hormonal contraception displayed higher levels of taurine-conjugated bile acids.

Conclusions

The novelty of the study is based on the identification of single bile acids during OLTT. LC-MS/MS-based quantification of bile acids in serum provides a reliable tool for future investigation of endocrine and metabolic effects of bile acids.

Mechanism of bile acid-regulated glucose and lipid metabolism in duodenal-jejunal bypass

Bile acid plays an important role in regulating blood glucose, lipid and energy metabolism. The present study was implemented to determine the effect of duodenal-jejunal bypass (DJB) on FXR, TGR-5expression in terminal ileum and its bile acid-related mechanism on glucose and lipid metabolism. Immunohistochemistry was used to detect relative gene or protein expression in liver and intestine. Firstly, we found that expression of FXR in liver and terminal ileum of DJB group was significantly higher than that in S-DJB group (P<0.05). In addition, DJB dramatically increased the activation of TGR-5 in the liver of rats. Furthermore, PEPCK, G6Pase, FBPase 1 and GLP-1 were up-regulated by DJB. In conclusion, these results showed that bile acid ameliorated glucose and lipid metabolism through bile acid-FXR and bile acid- TGR-5 signaling pathway.

The new biology of diabetes

Until recently, type 2 diabetes was seen as a disease caused by an impaired ability of insulin to promote the uptake and utilisation of glucose. Work on forkhead box protein O (FOXO) transcription factors revealed new aspects of insulin action that have led us to articulate a liver- and beta cell-centric narrative of diabetes pathophysiology and treatment. FOXO integrate a surprisingly diverse subset of biological functions to promote metabolic flexibility. In the liver, they controls the glucokinase/glucose-6-phosphatase switch and bile acid pool composition, directing carbons to glucose or lipid utilisation, thus providing a unifying mechanism for the two abnormalities of the diabetic liver: excessive glucose production and increased lipid synthesis and secretion. Moreover, FOXO are necessary to maintain beta cell differentiation, and diabetes development is associated with a gradual loss of FOXO function that brings about beta cell dedifferentiation. We proposed that dedifferentiation is the main cause of beta cell failure and conversion into non-beta endocrine cells, and that treatment should restore beta cell differentiation. Our studies investigating these proposals have revealed new dimensions to the pathophysiology of diabetes that can be leveraged to design new therapies.

In vitro and in vivo evaluation of novel cross-linked saccharide based polymers as bile acid sequestrants

Bile acid sequestrants (BAS) represent a therapeutic approach for the management of hypercholesterolemia that relies on the cationic polymeric nature of BAS to selectively bind negatively charged bile acids. We hypothesized that the cross-linking of β-cyclodextrin (β-CD) and saccharides such as starch or dextrin with divinyl sulfone (DVS) yields homo- and hetero-polymeric materials with the ability to trap sterols. Our hypothesis was put to test by synthesizing a library of 22 polymers that were screened to evaluate their capability to sequester both cholesterol (CHOL) and cholic and deoxycholic acids (CA and DCA). Three polymers synthesized in high yield were identified as promising. Two were neutral hetero-polymers of β-CD and starch or dextrin and the third was a weakly cationic homo-polymer of starch, highlighting the importance of the cavity effect. They were tested in hypercholesterolemic male Wistar rats and their ability to regulate hypercholesterolemia was similar to that for the reference BAS cholestyramine, but with two additional advantages: (i) they normalized the TG level and (ii) they did not increase the creatinine level. Neither hepatotoxicity nor kidney injury was detected, further supporting them as therapeutical candidates to manage hypercholesterolemia.

Lowering low-density lipoprotein cholesterol levels in patients with type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is characterized by hyperglycemia, insulin resistance, and/or progressive loss of β-cell function. T2DM patients are at increased risk of micro- and macrovascular disease, and are often considered as representing an atherosclerotic coronary heart disease (CHD) risk equivalent. Interventions directed at glucose and lipid level control in T2DM patients may reduce micro- and macrovascular disease. The optimal T2DM agent is one that lowers glucose levels with limited risk for hypoglycemia, and with no clinical trial evidence of worsening CHD risk. Lipid-altering drugs should preferably reduce low-density lipoprotein cholesterol and apolipoprotein B (apo B) and have evidence that the mechanism of action reduces CHD risk. Statins reduce low-density lipoprotein cholesterol and apo B and have evidence of improving CHD outcomes, and are thus first-line therapy for the treatment of hypercholesterolemia. In patients who do not achieve optimal lipid levels with statin therapy, or who are intolerant to statin therapy, add-on therapy or alternative therapies may be indicated. Additional available agents to treat hypercholesterolemic patients with T2DM include bile acid sequestrants, fibrates, niacin, and ezetimibe. This review discusses the use of these alternative agents to treat hypercholesterolemia in patients with T2DM, either as monotherapy or in combination with statin therapy.

Clostridium scindens: a human gut microbe with a high potential to convert glucocorticoids into androgens

Clostridium scindens American Type Culture Collection 35704 is capable of converting primary bile acids to toxic secondary bile acids, as well as converting glucocorticoids to androgens by side-chain cleavage. The molecular structure of the side-chain cleavage product of cortisol produced by C. scindens was determined to be 11β-hydroxyandrost-4-ene-3,17-dione (11β-OHA) by high-resolution mass spectrometry, ¹H and ¹³C NMR spectroscopy, and X-ray crystallography. Using RNA-Seq technology, we identified a cortisol-inducible (∼1,000-fold) operon (desABCD) encoding at least one enzyme involved in anaerobic side-chain cleavage. The desC gene was cloned, overexpressed, purified, and found to encode a 20α-hydroxysteroid dehydrogenase (HSDH). This operon also encodes a putative “transketolase” (desAB) hypothesized to have steroid-17,20-desmolase/oxidase activity, and a possible corticosteroid transporter (desD). RNA-Seq data suggests that the two-carbon side chain of glucocorticords may feed into the pentose-phosphate pathway and are used as a carbon source. The 20α-HSDH is hypothesized to function as a metabolic “rheostat” controlling rates of side-chain cleavage. Phylogenetic analysis suggests this operon is rare in nature and the desC gene evolved from a gene encoding threonine dehydrogenase. The physiological effect of 11β-OHAD on the host or other gut microbes is currently unknown.

Pleiotropic roles of bile acids in metabolism

Enzymatic oxidation of cholesterol generates numerous distinct bile acids that function both as detergents that facilitate digestion and absorption of dietary lipids, and as hormones that activate four distinct receptors. Activation of these receptors alters gene expression in multiple tissues, leading to changes not only in bile acid metabolism but also in glucose homeostasis, lipid and lipoprotein metabolism, energy expenditure, intestinal motility and bacterial growth, inflammation, liver regeneration, and hepatocarcinogenesis. This review covers the roles of specific bile acids, synthetic agonists, and their cognate receptors in controlling these diverse functions, as well as their current use in treating human diseases.

Epigenetics of insulin resistance: an emerging field in translational medicine

In this article, we review the current knowledge of and recent insights into the role of epigenetic factors in the development of insulin resistance (IR), with emphasis on peroxisome proliferator-activated receptor gamma coactivator 1α (PPARGC1A or PGC1α) methylation on fetal programming and liver modulation of glucose-related phenotypes. We discuss the pathogenesis of IR beyond the integrity of β-cell function and illustrate the novel concept of mitochondrial epigenetics to explain the pathobiology of metabolic-syndrome-related phenotypes. Moreover, we discuss whether epigenetic marks in genes of the circadian rhythm system are able to modulate insulin/glucose-related metabolic functions and place hypoxia inducible factor 1 α (HIF1α) as a part of the master CLOCK gene/protein interaction network that might modulate IR. Finally, we highlight relevant information about epigenetic marks and IR so that clinicians practicing in the community may envision future areas of medical intervention and predict putative biomarkers for early disease detection.

Persimmon fruit tannin-rich fiber reduces cholesterol levels in humans

Bile acid-binding agents are known to lower blood cholesterol levels and have been clinically used for the treatment of hypercholesterolemia. We previously showed that tannin-rich fiber from young persimmon (Diospyros kaki) fruits had bile acid-binding properties. In this study, we performed a randomized, double-blind, placebo-controlled trial to investigate the hypocholesterolemic effects of tannin-rich fiber in humans. The subjects (n = 40, plasma total cholesterol levels 180-259 mg/dl) were divided into 3 groups and ingested cookie bars containing 0 g (placebo group, n = 14), 3 g (low-dose group, n = 13), or 5 g (high-dose group, n = 13) of tannin-rich fiber 3 times daily before meals for 12 weeks. Plasma total cholesterol levels decreased significantly in the low-dose (12 weeks, p < 0.005) and high-dose (6 weeks, p < 0.05; 12 weeks, p < 0.001) groups. In addition, plasma low-density lipoprotein cholesterol levels decreased significantly in the high-dose group (6 weeks, p < 0.05; 12 weeks, p < 0.001). These improvements were not accompanied by changes in plasma high-density lipoprotein cholesterol or plasma triglyceride levels. Our findings indicate that tannin-rich fiber from young persimmon fruits is a useful food material for treating hypercholesterolemia.

Review article: the emerging interplay among the gastrointestinal tract, bile acids and incretins in the pathogenesis of diabetes and non-alcoholic fatty liver disease

BACKGROUND

Recent research has led to an interest in the role of the gut and liver in type 2 diabetes mellitus (T2DM).

AIM

To review the role of the gastrointestinal system in glucose homoeostasis, with particular focus on the effects of incretin hormones, hepatic steatosis and bile acids.

METHODS

PubMed and Google Scholar were searched using terms such as incretin, glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), dipeptidyl peptidase-4 (DPP-4), hepatic steatosis, bile acid and gastric bypass. Additional relevant references were identified by reviewing the reference lists of articles.

RESULTS

Perturbations of incretin hormones and bile acid secretion contribute to the pathogenesis of T2DM, leading to their potential as therapeutic targets. The incretin hormones (GIP and GLP-1) are deactivated by DPP-4. GLP-1 agonists and DPP-4 inhibitors improve glycaemic control in patients with T2DM. Hepatic steatosis, along with insulin resistance, may precede the development of T2DM, and may benefit from anti-diabetes medications. Bile acids play an important role in glucose homoeostasis, with effects mediated via the farnesoid X receptor (FXR) and the cell surface receptor TGR5. The bile acid sequestrant colesevelam has been shown to be effective in improving glycaemic control in patients with T2DM. Altered gastrointestinal anatomy after gastric bypass surgery may also affect enterohepatic recirculation of bile acids and contribute to improved glycaemic control.

CONCLUSIONS

Research in recent years has led to new pathways and processes with a role in glucose homoeostasis, and new therapeutic targets and options for type 2 diabetes mellitus.

Bile acids acutely stimulate insulin secretion of mouse β-cells via farnesoid X receptor activation and K(ATP) channel inhibition

Type 2 diabetes mellitus is associated with alterations in bile acid (BA) signaling. The aim of our study was to test whether pancreatic β-cells contribute to BA-dependent regulation of glucose homeostasis. Experiments were performed with islets from wild-type, farnesoid X receptor (FXR) knockout (KO), and β-cell ATP-dependent K(+) (K(ATP)) channel gene SUR1 (ABCC8) KO mice, respectively. Sodium taurochenodeoxycholate (TCDC) increased glucose-induced insulin secretion. This effect was mimicked by the FXR agonist GW4064 and suppressed by the FXR antagonist guggulsterone. TCDC and GW4064 stimulated the electrical activity of β-cells and enhanced cytosolic Ca(2+) concentration ([Ca(2+)](c)). These effects were blunted by guggulsterone. Sodium ursodeoxycholate, which has a much lower affinity to FXR than TCDC, had no effect on [Ca(2+)](c) and insulin secretion. FXR activation by TCDC is suggested to inhibit K(ATP) current. The decline in K(ATP) channel activity by TCDC was only observed in β-cells with intact metabolism and was reversed by guggulsterone. TCDC did not alter insulin secretion in islets of SUR1-KO or FXR-KO mice. TCDC did not change islet cell apoptosis. This is the first study showing an acute action of BA on β-cell function. The effect is mediated by FXR by nongenomic elements, suggesting a novel link between FXR activation and K(ATP) channel inhibition.