Metformin interferes with bile acid homeostasis through AMPK-FXR crosstalk

Metformin: Diverse molecular mechanisms, gastrointestinal effects and overcoming intolerance in type 2 Diabetes Mellitus: A review

Metformin, the first line treatment for patients with type 2 diabetes mellitus, has alternative novel roles, including cancer and diabetes prevention. This narrative review aims to explore its diverse mechanisms, effects and intolerance, using sources obtained by searching Scopus, PubMed and Web of Science databases, and following Scale for the Assessment of Narrative Review Articles reporting guidelines. Metformin exerts it actions through duration influenced, and organ specific, diverse mechanisms. Its use is associated with inhibition of hepatic gluconeogenesis targeted by mitochondria and lysosomes, reduction of cholesterol levels involving brown adipose tissue, weight reduction influenced by growth differentiation factor 15 and novel commensal bacteria, in addition to counteraction of meta-inflammation alongside immuno-modulation. Interactions with the gastrointestinal tract include alteration of gut microbiota, enhancement of glucose uptake and glucagon like peptide 1 and reduction of bile acid absorption. Though beneficial, they may be linked to intolerance. Metformin related gastrointestinal adverse effects are associated with dose escalation, immediate release formulations, gut microbiota alteration, epigenetic predisposition, inhibition of organic cation transporters in addition to interactions with serotonin, histamine and the enterohepatic circulation. Potentially effective measures to overcome intolerance encompasses carefully objective targeted dose escalation, prescription of fixed dose combination, microbiome modulators and prebiotics, in addition to use of extended release formulations.

Increased hepatic gluconeogenesis and type 2 diabetes mellitus

Abnormally increased hepatic gluconeogenesis is a significant contributor to hyperglycemia in the fasting state in patients with type 2 diabetes mellitus (T2DM) due to insulin resistance. Metformin, the most prescribed drug for the treatment of T2DM, is believed to exert its effect mainly by reducing hepatic gluconeogenesis. Here, we discuss how increased hepatic gluconeogenesis contributes to T2DM and we review newly revealed mechanisms underlying the attenuation of gluconeogenesis by metformin. In addition, we analyze the recent findings on new determinants involved in the regulation of gluconeogenesis, which might ultimately lead to the identification of novel and targeted treatment strategies for T2DM.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Understanding the action mechanisms of metformin in the gastrointestinal tract

Metformin is the initial medication recommended for the treatment of type 2 diabetes mellitus (T2DM). In addition to diabetes treatment, the function of metformin also can be anti-aging, antiviral, and anti-inflammatory. Nevertheless, further exploration is required to fully understand its mode of operation. Historically, the liver has been acknowledged as the main location where metformin reduces glucose levels, however, there is increasing evidence suggesting that the gastrointestinal tract also plays a significant role in its action. In the gastrointestinal tract, metformin effects glucose uptake and absorption, increases glucagon-like peptide-1 (GLP-1) secretion, alters the composition and structure of the gut microbiota, and modulates the immune response. However, the side effects of it cannot be ignored such as gastrointestinal distress in patients. This review outlines the impact of metformin on the digestive system and explores potential explanations for variations in metformin effectiveness and adverse effects like gastrointestinal discomfort.

Benefits of Monascus anka solid-state fermentation for quinoa polyphenol bioaccessibility and the anti-obesity effect linked with gut microbiota

In our previous study, a polyphenol-utilization targeted quinoa product was developed via solid-state fermentation with Monascus anka. In this study, we investigated the polyphenol-related novel functions of the fermented product further. Compared with unfermented quinoa, M. anka fermented quinoa alleviated the trapping effect of the macromolecules, especially in the colonic fermentation stage, resulting in enhanced polyphenol bioaccessibility. Lachnoclostridium, Megasphaera, Megamonas, Dialister, and Phascolarctobacterium might contribute to polyphenol liberation and metabolism in fermented quinoa. Additionally, fermented quinoa polyphenols presented an efficient anti-obesity effect by enhancing hepatic antioxidant enzyme activities, suppressing fatty acid synthesis, accelerating fatty acid oxidation, and improving bile acid synthesis. Moreover, fermented quinoa polyphenol supplementation alleviated gut microbiota disorder induced by a high-fat diet, resulting in a decreased ratio of Firmicutes/Bacteroidota, and increased relative abundances of Lactobacillus and Lachnoclostridium. The obtained results suggested that the principal anti-obesity effect of fermented quinoa polyphenols might act through the AMPK/PPARα/CPT-1 pathway. In conclusion, M. anka solid-state fermentation effectively enhanced the bioaccessibility of quinoa, and the fermented quinoa polyphenols showed considerable anti-obesity effect. Our findings provide new perspectives for the development of dietary polyphenol-based satiety-enhancing functional foods.

High-throughput transcriptomics of 409 bacteria-drug pairs reveals drivers of gut microbiota perturbation

Many drugs can perturb the gut microbiome, potentially leading to negative health consequences. However, mechanisms of most microorganism-drug responses have not been elucidated at the genetic level. Using high-throughput bacterial transcriptomics, we systematically characterized the gene expression profiles of prevalent human gut bacteria exposed to the most frequently prescribed orally administered pharmaceuticals. Across >400 drug-microorganism pairs, significant and reproducible transcriptional responses were observed, including pathways involved in multidrug resistance, metabolite transport, tartrate metabolism and riboflavin biosynthesis. Importantly, we discovered that statin-mediated upregulation of the AcrAB-TolC efflux pump in Bacteroidales species enhances microbial sensitivity to vitamin A and secondary bile acids. Moreover, gut bacteria carrying acrAB-tolC genes are depleted in patients taking simvastatin, suggesting that drug-efflux interactions generate collateral toxicity that depletes pump-containing microorganisms from patient microbiomes. This study provides a resource to further understand the drivers of drug-mediated microbiota shifts for better informed clinical interventions.

Effects of Medications on Heat Loss Capacity in Chronic Disease Patients: Health Implications Amidst Global Warming

Pharmacological agents used to treat or manage diseases can modify the level of heat strain experienced by chronically ill and elderly patients via different mechanistic pathways. Human thermoregulation is a crucial homeostatic process that maintains body temperature within a narrow range during heat stress through dry (i.e., increasing skin blood flow) and evaporative (i.e., sweating) heat loss, as well as active inhibition of thermogenesis, which is crucial to avoid overheating. Medications can independently and synergistically interact with aging and chronic disease to alter homeostatic responses to rising body temperature during heat stress. This review focuses on the physiologic changes, with specific emphasis on thermolytic processes, associated with medication use during heat stress. The review begins by providing readers with a background of the global chronic disease burden. Human thermoregulation and aging effects are then summarized to give an understanding of the unique physiologic changes faced by older adults. The effects of common chronic diseases on temperature regulation are outlined in the main sections. Physiologic impacts of common medications used to treat these diseases are reviewed in detail, with emphasis on the mechanisms by which these medications alter thermolysis during heat stress. The review concludes by providing perspectives on the need to understand the effects of medication use in hot environments, as well as a summary table of all clinical considerations and research needs of the medications included in this review. SIGNIFICANCE STATEMENT: Long-term medications modulate thermoregulatory function, resulting in excess physiological strain and predisposing patients to adverse health outcomes during prolonged exposures to extreme heat during rest and physical work (e.g., exercise). Understanding the medication-specific mechanisms of altered thermoregulation has importance in both clinical and research settings, paving the way for work toward refining current medication prescription recommendations and formulating mitigation strategies for adverse drug effects in the heat in chronically ill patients.

Striking a gut-liver balance for the antidiabetic effects of metformin

Metformin is the most prescribed drug for the treatment of type 2 diabetes mellitus (T2DM), but its mechanism of action has not yet been completely elucidated. Classically, the liver has been considered the major site of action of metformin. However, over the past few years, advances have unveiled the gut as an additional important target of metformin, which contributes to its glucose-lowering effect through new mechanisms of action. A better understanding of the mechanistic details of metformin action in the gut and the liver and its relevance in patients remains the challenge of present and future research and may impact drug development for the treatment of T2DM. Here, we offer a critical analysis of the current status of metformin-driven multiorgan glucose-lowering effects.

Pharmacological management of youth with type 2 diabetes and diabetic kidney disease: a comprehensive review of current treatments and future directions

INTRODUCTION

Diabetic kidney disease (DKD) is a leading cause of mortality in people with type 2 diabetes (T2D), and over 50% of individuals with youth-onset T2D will develop DKD as a young adult. Diagnosis of early-onset DKD remains a challenge in young persons with T2D secondary to a lack of available biomarkers for early DKD, while the injuries may still be reversible. Furthermore, multiple barriers exist to initiate timely prevention and treatment strategies for DKD, including a lack of Food and Drug Administration approval of medications in pediatrics; provider comfort with medication prescription, titration, and monitoring; and medication adherence.

AREAS COVERED

Therapies that have promise for slowing DKD progression in youth with T2D include metformin, renin-angiotensin-aldosterone system inhibitors, glucagon-like peptide-1 receptor agonists, sodium glucose co-transporter 2 inhibitors, thiazolidinediones, sulfonylureas, endothelin receptor agonists, and mineralocorticoid antagonists. Novel agents are also in development to act synergistically on the kidneys with the aforementioned medications. We comprehensively review the available pharmacologic strategies for DKD in youth-onset T2D including mechanisms of action, potential adverse effects, and kidney-specific effects, with an emphasis on published pediatric and adult trials.

EXPERT OPINION

Large clinical trials evaluating pharmacologic interventions targeting the treatment of DKD in youth-onset T2D are strongly needed.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Interactions between Intestinal Homeostasis and NAD+ Biology in Regulating Incretin Production and Postprandial Glucose Metabolism

The intestine has garnered attention as a target organ for developing new therapies for impaired glucose tolerance. The intestine, which produces incretin hormones, is the central regulator of glucose metabolism. Glucagon-like peptide-1 (GLP-1) production, which determines postprandial glucose levels, is regulated by intestinal homeostasis. Nicotinamide phosphoribosyltransferase (NAMPT)-mediated nicotinamide adenine dinucleotide (NAD⁺) biosynthesis in major metabolic organs such as the liver, adipose tissue, and skeletal muscle plays a crucial role in obesity- and aging-associated organ derangements. Furthermore, NAMPT-mediated NAD⁺ biosynthesis in the intestines and its upstream and downstream mediators, adenosine monophosphate-activated protein kinase (AMPK) and NAD⁺-dependent deacetylase sirtuins (SIRTs), respectively, are critical for intestinal homeostasis, including gut microbiota composition and bile acid metabolism, and GLP-1 production. Thus, boosting the intestinal AMPK-NAMPT-NAD⁺-SIRT pathway to improve intestinal homeostasis, GLP-1 production, and postprandial glucose metabolism has gained significant attention as a novel strategy to improve impaired glucose tolerance. Herein, we aimed to review in detail the regulatory mechanisms and importance of intestinal NAMPT-mediated NAD⁺ biosynthesis in regulating intestinal homeostasis and GLP-1 secretion in obesity and aging. Furthermore, dietary and molecular factors regulating intestinal NAMPT-mediated NAD⁺ biosynthesis were critically explored to facilitate the development of new therapeutic strategies for postprandial glucose dysregulation.

Role of FXR in Renal Physiology and Kidney Diseases

Farnesoid X receptor, also known as the bile acid receptor, belongs to the nuclear receptor (NR) superfamily of ligand-regulated transcription factors, which performs its functions by regulating the transcription of target genes. FXR is highly expressed in the liver, small intestine, kidney and adrenal gland, maintaining homeostasis of bile acid, glucose and lipids by regulating a diverse array of target genes. It also participates in several pathophysiological processes, such as inflammation, immune responses and fibrosis. The kidney is a key organ that manages water and solute homeostasis for the whole body, and kidney injury or dysfunction is associated with high morbidity and mortality. In the kidney, FXR plays an important role in renal water reabsorption and is thought to perform protective functions in acute kidney disease and chronic kidney disease, especially diabetic kidney disease. In this review, we summarize the recent advances in the understanding of the physiological and pathophysiological function of FXR in the kidney.

AMPK inhibits liver gluconeogenesis: fact or fiction?

Is there a role for AMPK in the control of hepatic gluconeogenesis and could targeting AMPK in liver be a viable strategy for treating type 2 diabetes? These are frequently asked questions this review tries to answer. After describing properties of AMPK and different small-molecule AMPK activators, we briefly review the various mechanisms for controlling hepatic glucose production, mainly via gluconeogenesis. The different experimental and genetic models that have been used to draw conclusions about the role of AMPK in the control of liver gluconeogenesis are critically discussed. The effects of several anti-diabetic drugs, particularly metformin, on hepatic gluconeogenesis are also considered. We conclude that the main effect of AMPK activation pertinent to the control of hepatic gluconeogenesis is to antagonize glucagon signalling in the short-term and, in the long-term, to improve insulin sensitivity by reducing hepatic lipid content.

Gut microbiota is correlated with gastrointestinal adverse events of metformin in patients with type 2 diabetes

Aim

Gastrointestinal discomfort is the most common adverse event in metformin treatment for type 2 diabetes. The mechanism of action of metformin is associated with gut microbiota. However, the gut microbial community structure related to metformin-induced gastrointestinal adverse events remains unclear. This study aimed to investigate it.

Methods

50 patients with newly diagnosed diabetes were treated with metformin 1500mg/d for 12 weeks. The patients were divided into two groups according to whether gastrointestinal adverse events occurred (group B) or did not occur (group A) after treatment. The fecal bacterial communities and short-chain fatty acids (SCFAs) were sequenced and compared. 70 diabetes mice were randomly divided into 8 groups and treated with metformin (Met), clindamycin (Clin) and/or SCFA, which were the Met+/Clin+, Met+/Clin-, Met-/Clin+, Met-/Clin-, Met+/SCFA+, Met+/SCFA-, Met-/SCFA+ and Met-/SCFA- group. After 4 weeks of metformin treatment, blood glucose, food intake, fecal SCFAs, gut microbiota and gut hormones were measured.

Results

Metformin increased the abundance of Phascolarctobacterium, Intestinimonas and Clostridium III. Functional prediction analysis showed that the propanoate metabolism pathway was significantly up-regulated. The concentrations of acetic acid and propanoic acid in feces were significantly increased. The abundance of Clostridium sensu stricto, Streptococcus and Akkermansia induced by metformin in group B was higher than that in group A. The propanoate metabolism pathway and propanoic acid in feces were significantly up-regulated in group B. In the animal experiments, the food intake decreased and glucose control increased in metformin groups compared with those in the control groups. The total GLP-1 level in the Met+/Clin- group was significantly higher than that in the Met-/Clin- group, while there was no statistical difference between the Met-/Clin- and Met+/Clin+ group. The total GLP-1 level in the Met-/SCFA+ group was significantly higher than that in the Met-/SCFA-group, while the levels of total GLP-1 and active GLP-1 in the Met+/SCFA- group and the Met+/SCFA+ group were significantly higher than those in the Met-/SCFA-group.

Conclusions

Our data suggest that metformin promotes the secretion of intestinal hormones such as GLP-1 by increasing the abundance of SCFA-producing bacteria, which not only plays an anti-diabetic role, but also may causes gastrointestinal adverse events.

Obesity-induced miR-802 directly targets AMPK and promotes nonalcoholic steatohepatitis in mice

OBJECTIVE

Obesity-associated nonalcoholic fatty liver disease (NAFLD) is a leading cause of liver failure and death. However, the pathogenesis of NAFLD and its severe form, nonalcoholic steatohepatitis (NASH), is poorly understood. The energy sensor, AMP-activated protein kinase (AMPK), has decreased activity in obesity and NAFLD, but the mechanisms are unclear. Here, we examined whether obesity-induced miR-802 has a role in promoting NASH by targeting AMPK. We also investigated whether miR-802 and AMPK have roles in modulating beneficial therapeutic effects mediated by obeticholic acid (OCA), a promising clinical agent for NASH.

METHODS

Immunoblotting, luciferase assays, and RNA-protein interaction studies were performed to test whether miR-802 directly targets AMPK. The roles of miR-802 and AMPK in NASH were examined in mice fed a NASH-promoting diet.

RESULTS

Hepatic miR-802 and AMPK levels were inversely correlated in both NAFLD patients and obese mice. MicroRNA in silico analysis, together with biochemical studies in hepatic cells, suggested that miR-802 inhibits hepatic expression of AMPK by binding to the 3' untranslated regions of both human AMPKα1 and mouse Ampkβ1. In diet-induced NASH mice, OCA treatment reduced hepatic miR-802 levels and improved AMPK activity, ameliorating steatosis, inflammation, and apoptosis, but these OCA-mediated beneficial effects on NASH pathologies, particularly reducing apoptosis, were reversed by overexpression of miR-802 or downregulation of AMPK.

CONCLUSIONS

These results indicate that miR-802 inhibits AMPK by directly targeting Ampkβ1, promoting NAFLD/NASH in mice. The miR-802-AMPK axis that modulates OCA-mediated beneficial effects on NASH may represent a new therapeutic target.

Deciphering metformin action in obese mice: A critical re-evaluation of established protocols

BACKGROUND AND PURPOSE

Despite extensive efforts and a plethora of suggested targets and pathways, the mechanism via which metformin lowers blood glucose remains obscure. Obstacles that hamper progress in understanding metformin action include unexplained discrepancies between preclinical models and patients.

PROCEDURES

We treated obese male C57BL/6J mice fed high fat diet with metformin provided in the form of a single dose, daily intraperitoneal injections, admixture to drinking water, or continuous infusion via intraperitoneal minipumps.

RESULTS

The results suggest several superimposed components, via which metformin acts on blood glucose. These include (i) marked glucose lowering shortly after dosing, which fades rapidly with the decrease in metformin concentrations in plasma and liver, but could, at least to a major extent, rely on the mechanism also accounting for metformin's therapeutic action in humans; (ii) indirect action via reduced weight gain, which might be responsible for glucose lowering observed in many previous rodent studies; and (iii) deterioration of glucose homeostasis by prolonged treatment that can be unmasked by avoidance of dosing shortly before measuring blood glucose in combination with exclusion of weight-related actions via restricted feeding of the control mice.

CONCLUSIONS

Our work raises the question whether elucidation of metformin's anti-diabetic mechanism(s) in rodent experiments may in the past have been hampered by failure to mimic clinical circumstances, as caused by insufficient consideration of pharmacokinetics and multiplicity of involved actions.

Development of an adverse outcome pathway for intrahepatic cholestasis of pregnancy

Adverse Outcome Pathways (AOPs) are a research synthesis tool, used primarily by toxicologists for numerous applications including: hypothesis generation, data integration, biomarker determination, and identification of gaps in current knowledge. The AOP model provides a means for evaluating critical interactions between stressors and biological systems which result in adversity, meaning there is significant potential value in using this model in clinical research. However, AOPs have so far not been applied in this context, which may be attributable to the fact that the method is not yet streamlined with established practices in evidence-based medicine, such as systematic review. Here, we present one approach to developing a clinically focused AOP for intrahepatic cholestasis of pregnancy; aiming to enhance understanding of the mechanistic link between this common, gestational liver disease and its association with preterm birth. Mechanistic aspects of the disease pathogenesis, and use of AOPs to broaden inclusion and improve integration of in vitro and in vivo data in clinical research are discussed. We also demonstrate for the first time how central components of systematic review can be integrated into the development of an AOP.

Beneficial Activities of Alisma orientale Extract in a Western Diet-Induced Murine Non-Alcoholic Steatohepatitis and Related Fibrosis Model via Regulation of the Hepatic Adiponectin and Farnesoid X Receptor Pathways

The hepatic adiponectin and farnesoid X receptor (FXR) signaling pathways play multiple roles in modulating lipid and glucose metabolism, reducing hepatic inflammation and fibrosis, and altering various metabolic targets for the management of non-alcoholic fatty liver disease (NAFLD). Alisma orientale (AO, Ze xie in Chinese and Taeksa in Korean) is an herbal plant whose tubers are enriched with triterpenoids, which have been reported to exhibit various bioactive properties associated with NAFLD. Here, the present study provides a preclinical evaluation of the biological functions and related signaling pathways of AO extract for the treatment of NAFLD in a Western diet (WD)-induced mouse model. The findings showed that AO extract significantly reversed serum markers (liver function, lipid profile, and glucose) and improved histological features in the liver sections of mice fed WD for 52 weeks. In addition, it also reduced hepatic expression of fibrogenic markers in liver tissue and decreased the extent of collagen-positive areas, as well as inhibited F4/80 macrophage aggregation and inflammatory cytokine secretion. The activation of adiponectin and FXR expression in hepatic tissue may be a major mechanistic signaling cascade supporting the promising role of AO in NAFLD pharmacotherapy. Collectively, our results demonstrated that AO extract improves non-alcoholic steatohepatitis (NASH) resolution, particularly with respect to NASH-related fibrosis, along with the regulation of liver enzymes, postprandial hyperglycemia, hyperlipidemia, and weight loss, probably through the modulation of the hepatic adiponectin and FXR pathways.

LKB1 in Intestinal Epithelial Cells Regulates Bile Acid Metabolism by Modulating FGF15/19 Production

BACKGROUND & AIMS

Liver kinase B1 (LKB1) is a master upstream protein kinase involved in nutrient sensing and glucose and lipid metabolism in many tissues; however, its metabolic role in intestinal epithelial cells (IEC) remains unclear. In this study, we investigated the regulatory role of LKB1 on bile acid (BA) homeostasis.

METHODS

We generated mice with IEC-specific deletion of LKB1 (LKB1^ΔIEC) and analyzed the characteristics of IEC development and BA level. In vitro assays with small interfering RNA, liquid chromatography/mass spectrometry, metagenomics, and RNA-sequencing were used to elucidate the regulatory mechanisms underlying perturbed BA homeostasis.

RESULTS

LKB1 deletion resulted in abnormal differentiation of secretory cell lineages. Unexpectedly, BA pool size increased substantially in LKB1^ΔIEC mice. A significant reduction of the farnesoid X receptor (FXR) target genes, including fibroblast growth factor 15/19 (FGF15/19), known to inhibit BA synthesis, was found in the small intestine (SI) ileum of LKB1^ΔIEC mice. We observed that LKB1 depletion reduced FGF15/19 protein level in human IECs in vitro. Additionally, a lower abundance of bile salt hydrolase-producing bacteria and elevated levels of FXR antagonist (ie, T-βMCA) were observed in the SI of LKB1^ΔIEC mice. Moreover, LKB1^ΔIEC mice showed impaired conversion of retinol to retinoic acids in the SI ileum. Subsequently, vitamin A treatment failed to induce FGF15 production. Thus, LKB1^ΔIEC mice fed with a high-fat diet showed improved glucose tolerance and increased energy expenditure.

CONCLUSIONS

LKB1 in IECs manages BA homeostasis by controlling FGF15/19 production.

Integrated or Independent Actions of Metformin in Target Tissues Underlying Its Current Use and New Possible Applications in the Endocrine and Metabolic Disorder Area

Metformin is considered the first-choice drug for type 2 diabetes treatment. Actually, pleiotropic effects of metformin have been recognized, and there is evidence that this drug may have a favorable impact on health beyond its glucose-lowering activity. In summary, despite its long history, metformin is still an attractive research opportunity in the field of endocrine and metabolic diseases, age-related diseases, and cancer. To this end, its mode of action in distinct cell types is still in dispute. The aim of this work was to review the current knowledge and recent findings on the molecular mechanisms underlying the pharmacological effects of metformin in the field of metabolic and endocrine pathologies, including some endocrine tumors. Metformin is believed to act through multiple pathways that can be interconnected or work independently. Moreover, metformin effects on target tissues may be either direct or indirect, which means secondary to the actions on other tissues and consequent alterations at systemic level. Finally, as to the direct actions of metformin at cellular level, the intracellular milieu cooperates to cause differential responses to the drug between distinct cell types, despite the primary molecular targets may be the same within cells. Cellular bioenergetics can be regarded as the primary target of metformin action. Metformin can perturb the cytosolic and mitochondrial NAD/NADH ratio and the ATP/AMP ratio within cells, thus affecting enzymatic activities and metabolic and signaling pathways which depend on redox- and energy balance. In this context, the possible link between pyruvate metabolism and metformin actions is extensively discussed.

Policosanol alleviates hepatic lipid accumulation by regulating bile acids metabolism in C57BL6/mice through AMPK-FXR-TGR5 cross-talk

Policosanol exhibits a lipid accumulation alleviating effect, but the underlying mechanisms remains unclear. Bile acids are a significant factor in regulating cholesterol and lipid metabolism homeostasis in mammals. This study was aimed to elucidate the alleviating effect and underlying mechanisms of policosanol on hepatic lipid accumulation through bile acid (BA) metabolism. Policosanol supplementation significantly reduced hepatic triglycerides (19.29%), cholesterol (30.38%) in high fat diet (HFD) induced obese mice (P < 0.05). Furthermore, compared with the control group, HFD decreased the levels of total BAs (TBAs, 37.67%) and cholic acid (CA, 62.74%) in the serum of mice (P < 0.05). Meanwhile, compared to HFD group, policosanol also increased the level of secondary BAs (SBAs) and muricholic acids (MCAs, P < 0.05). qRT-PCR combined with protein level analysis revealed that policosanol significantly decreased sterol regulatory element-binding protein (SREBP-1c) and CD36, and increased the expression level of cytochrome P450 family 7 subfamily A member 1 (CYP7A1) and cytochrome P450 Family 27 Subfamily A Member 1 (CYP27A1, P < 0.05). Additionally, in the liver, policosanol was found downregulated the expression of farnesoid X receptor (FXR)-small heterodimer partner (SHP), and activate the Takeda G-coupled protein receptor 5 (TGR5)-adenosine-monophosphate-activated protein kinase (APMK) signaling pathway (P < 0.05). Peroxisome proliferator activated receptor (PPAR)-α, hormone sensitive lipase (HSL), and carnitine palmitoyltransferase (CPT)-1α also significantly increased in HP group (P < 0.05). The aforementioned results reveal that the potential mechanism of policosanol in alleviating liver lipid accumulation is to promote BA synthesis and lipolysis through regulating the cross-talk of the AMPK-FXR-TGR5. New insight for the application of policosanol as an anti-fatty liver functional food ingredient or supplement is also provided. PRACTICAL APPLICATION: Policosanol is an important active component of cereals and insect waxes (15-80%). However, almost no policosanol in refined foods such as clear corn germ oil and wheat flour. This study showed that oral administration of policosanol can significantly reduce triglyceride and cholesterol levels in the liver through affecting AMPK-TGR5-FXR cross-talk, whereas no significant toxicological effect is reported in human and mouse models. This study may provide theoretical support for the theory of dietary structure and the development of dietary supplements to improve lipid metabolism targeting the "bile acid-AMPK-TGR5" pathway.

Involvement of Autophagy in Ageing and Chronic Cholestatic Diseases

Autophagy is a “housekeeping” lysosomal degradation process involved in numerous physiological and pathological processes in all eukaryotic cells. The dysregulation of hepatic autophagy has been described in several conditions, from obesity to diabetes and cholestatic disease. We review the role of autophagy, focusing on age-related cholestatic diseases, and discuss its therapeutic potential and the molecular targets identified to date. The accumulation of toxic BAs is the main cause of cell damage in cholestasis patients. BAs and their receptor, FXR, have been implicated in the regulation of hepatic autophagy. The mechanisms by which cholestasis induces liver damage include mitochondrial dysfunction, oxidative stress and ER stress, which lead to cell death and ultimately to liver fibrosis as a compensatory mechanism to reduce the damage. The stimulation of autophagy seems to ameliorate the liver damage. Autophagic activity decreases with age in several species, whereas its basic extends lifespan in animals, suggesting that it is one of the convergent mechanisms of several longevity pathways. No strategies aimed at inducing autophagy have yet been tested in cholestasis patients. However, its stimulation can be viewed as a novel therapeutic strategy that may reduce ageing-dependent liver deterioration and also mitigate hepatic steatosis.

An Integrated Bile Acids Profile Determination by UHPLC-MS/MS to Identify the Effect of Bile Acids Supplement in High Plant Protein Diet on Common Carp (Cyprinus carpio)

Bile acids (BAs) have considerable importance in the metabolism of glycolipid and cholesterol. The purpose of the present study is to clarify the effects of bile acids supplementary in a high plant protein diet for the common carp BA profiles and hepatopancreas and intestine health. An 11-week feeding trial was conducted with high plant protein diet (18% soybean meal and 18% cottonseed protein concentrated) (HP) and HP added 600 mg/kg BAs (HP+BAs) for common carp, and then, the UHPLC-MS/MS technology was used to analyze the BAs in the bile and plasma of two groups. HP could induce vacuolation of hepatocytes and accumulation of glycogen in the common carp, while these phenotypes were significantly improved in the HP+BAs group. In addition, the BA profile of the HP group and HP+BAs group are described in detail, for the common carp bile with treatment by exogenous BAs, TCA, CA, TβMCA, and TωMCA were the main components. Furthermore, in the HP+BAs group plasma, CDCA, CA, LCA, and GCDCA increased significantly; they could activate TGR5, and the activation of hepatopancreas TGR5 might regulate glucose metabolism to relieve hepatopancreas glycogen accumulation. This study proved that BAs supplemented to plant protein diet could relieve the common carp hepatopancreas glycogen accumulation by changing the BAs’ profile, thereby promoting its healthy growth, which has important guiding significance for the promotion of aquaculture development and makes an important contribution to expanding the strategic space of food security.

Meta-analysis and Consolidation of Farnesoid X Receptor Chromatin Immunoprecipitation Sequencing Data Across Different Species and Conditions

Farnesoid X receptor (FXR) is a nuclear receptor that controls gene regulation of different metabolic pathways and represents an upcoming drug target for various liver diseases. Several data sets on genome-wide FXR binding in different species and conditions exist. We have previously reported that these data sets are heterogeneous and do not cover the full spectrum of potential FXR binding sites. Here, we report the first meta-analysis of all publicly available FXR chromatin immunoprecipitation sequencing (ChIP-seq) data sets from mouse, rat, and human across different conditions using a newly generated analysis pipeline. All publicly available single data sets were biocurated in a standardized manner and compared on every relevant level from raw reads to affected functional pathways. Individual murine data sets were then virtually merged into a single unique "FXR binding atlas" spanning all potential binding sites across various conditions. Comparison of the single biocurated data sets showed that the overlap of FXR binding sites between different species is modest and ranges from 48% (mouse-human) to 55% (mouse-rat). Moreover, in vivo data among different species are more similar than human in vivo data compared to human in vitro data. The consolidated murine global FXR binding atlas virtually increases sequencing depth and allows recovering more and novel potential binding sites and signaling pathways that were missed in the individual data sets. The FXR binding atlas is publicly searchable (https://fxratlas.tugraz.at). Conclusion: Published single FXR ChIP-seq data sets and large-scale integrated omics data sets do not cover the full spectrum of FXR binding. Combining different individual data sets and creating an "FXR super-binding atlas" enhances understanding of FXR signaling capacities across different conditions. This is important when considering the potential wide spectrum for drugs targeting FXR in liver diseases.

Current understanding of autophagy in intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy (ICP) is the most common liver disease during pregnancy. Manifested with pruritus and elevation in bile acids, the etiology of ICP is still poorly understood. Although ICP is considered relatively benign for the mother, increased rates of adverse fetal outcomes including sudden fetal demise are possible devastating outcomes associated with ICP. Limited understanding of the underlying mechanisms restricted treatment options and managements of ICP. In recent decades, evolving evidence indicated the significance of autophagy in pregnancy and pregnancy complications. Autophagy is an ancient self-defense mechanism which is essential for cell survival, differentiation and development. Autophagy has pivotal roles in embryogenesis, implantation, and maintenance of pregnancy, and is involved in the orchestration of diverse physiological and pathological cellular responses in patients with pregnancy complications. Recent advances in these research fields provide tantalizing targets on autophagy to improve the care of pregnant women. This review summarizes recent advances in understanding autophagy in ICP and its possible roles in the causation and prevention of ICP.

Sargassum fusiforme fucoidan alleviates diet-induced insulin resistance by inhibiting colon-derived ceramide biosynthesis

Sargassum fusiforme fucoidan (SFF) is a highly sulfated heteropolysaccharide with various biological activities. As one of the causative factors of type 2 diabetes mellitus (T2DM), insulin resistance has become a global health issue. In this study, we investigated the potential pharmacological mechanisms by which SFF ameliorates insulin resistance in high-fat diet (HFD)-fed mice. SFF significantly enhanced tauroursodeoxycholic acid (TUDCA, a conjugated bile acid) levels and inhibited the farnesoid X receptor (FXR) signaling in the colon. SFF administration reduced ceramide levels in both serum and colonic tissue of HFD-fed mice, as well as reduced expression of SPT and CerS genes, which encode enzymes crucial to the biosynthesis of ceramides regulated by FXR signaling. Pearson's analysis showed that the TUDCA level was positively correlated with the gut bacteria Clostridium, and this was further validated in pseudo-germfree mice. Taken together, the results suggested that SFF increased TUDCA levels by remodeling gut microbiota, and TUDCA, a natural FXR antagonist, inhibited the FXR/SHP signaling pathway to reduce colon-derived biosynthesis of ceramide, thereby improving insulin resistance in the diet-induced obese (DIO) mice. This study has provided new insights into the therapeutic potential of S. fusiforme fucoidan in metabolic diseases.

An optimized protocol with a stepwise approach to identify specific nuclear receptor ligands from cultured mammalian cells

Here, we describe an optimized protocol to identify specific nuclear receptor ligands. First, to rule out any compound interference with luciferase activity per se, we describe an in vitro assay assessing potential inhibition or activation of luciferase enzymatic activity. Second, to comply with EMA and FDA guidelines to mitigate drug-drug interactions, we detail assays assessing constitutive androstane receptor (CAR) and pregnane X receptor (PXR) activation ability. Finally, to minimize off-target detection effects, we describe the use of mammalian one- (or two-) hybrid systems. For complete details on the use and execution of this protocol, please refer to Hering et al. (2018).

Metformin treatment for 8 days impacts multiple intestinal parameters in high-fat high-sucrose fed mice

Although the mechanism of action of the antidiabetic drug metformin is still a matter of discussions, it is well accepted that the gut plays an important role. To gain more insights into the mechanisms occurring in the different regions of the intestine, adult male mice were fed a high-fat-high sucrose (HFS) diet for 8 days and treated with metformin by gavage (300 mg/day/kg body weight) during the HFS diet. Metformin counteracted HFS diet-induced overexpression of a network of genes involved in the transport of glucose and fatty acids in the different regions of the small intestine. It also induced beneficial modification of secondary bile acid profile in the caecum, with a reduction of deoxycholic acid and lithocholic acid levels and increased abundance of ursodeoxycholic acid and tauroursodeoxycholic acid, potentially leading to FRX inhibition. In parallel, metformin treatment was associated with specific changes of the microbiota composition in the lumen of the different regions of the intestine. Metformin induced a marked increase in the abundance of Akkermansia muciniphila in the lumen all along the gut and counteracted the effects of HFS diet on the abundances of some bacterial groups generally associated with metabolic disturbances (f-Lachnospiraceae, f-Petostreptococcaceae, g-Clostidium). Therefore, the present work clearly emphasises the role of all the regions of the intestinal tract in the beneficial action of the antidiabetic drug metformin in a prediabetic mouse model.

Targeting Farnesoid X receptor (FXR) for developing novel therapeutics against cancer

Cancer is one of the lethal diseases that arise due to the molecular alterations in the cell. One of those alterations associated with cancer corresponds to differential expression of Farnesoid X receptor (FXR), a nuclear receptor regulating bile, cholesterol homeostasis, lipid, and glucose metabolism. FXR is known to regulate several diseases, including cancer and cardiovascular diseases, the two highly reported causes of mortality globally. Recent studies have shown the association of FXR overexpression with cancer development and progression in different types of cancers of breast, lung, pancreas, and oesophagus. It has also been associated with tissue-specific and cell-specific roles in various cancers. It has been shown to modulate several cell-signalling pathways such as EGFR/ERK, NF-κB, p38/MAPK, PI3K/AKT, Wnt/β-catenin, and JAK/STAT along with their targets such as caspases, MMPs, cyclins; tumour suppressor proteins like p53, C/EBPβ, and p-Rb; various cytokines; EMT markers; and many more. Therefore, FXR has high potential as novel biomarkers for the diagnosis, prognosis, and therapy of cancer. Thus, the present review focuses on the diverse role of FXR in different cancers and its agonists and antagonists.

The Hormetic Effect of Metformin: "Less Is More"?

Metformin (MTF) is the first-line therapy for type 2 diabetes (T2DM). The euglycemic effect of MTF is due to the inhibition of hepatic glucose production. Literature reports that the principal molecular mechanism of MTF is the activation of 5′-AMP-activated protein kinase (AMPK) due to the decrement of ATP intracellular content consequent to the inhibition of Complex I, although this effect is obtained only at millimolar concentrations. Conversely, micromolar MTF seems to activate the mitochondrial electron transport chain, increasing ATP production and limiting oxidative stress. This evidence sustains the idea that MTF exerts a hormetic effect based on its concentration in the target tissue. Therefore, in this review we describe the effects of MTF on T2DM on the principal target organs, such as liver, gut, adipose tissue, endothelium, heart, and skeletal muscle. In particular, data indicate that all organs, except the gut, accumulate MTF in the micromolar range when administered in therapeutic doses, unmasking molecular mechanisms that do not depend on Complex I inhibition.

Metformin impairs bile acid homeostasis in ethinylestradiol-induced cholestasis in mice

Metformin, an oral antidiabetic drug, recently demonstrated a reducing effect on bile acids (BA) plasma concentrations in one patient with intrahepatic cholestasis of pregnancy (ICP) by unknown mechanism. Therefore, the aim of the present study was to examine the effect of metformin on BA homeostasis and related molecular pathways in the liver and intestine using a mouse model of ICP. The cholestasis was induced in female C57BL/6 mice by repeated administration of ethinylestradiol (10 mg/kg BW s.c.) and/or metformin (150 mg/kg BW orally) over 5 consecutive days with subsequent bile collection and molecular analysis of samples. We demonstrated that metformin significantly increased the rate of bile secretion in control mice. This increase was BA dependent and was produced both by increased liver BA synthesis via induced cholesterol 7α-hydroxylase (Cyp7a1) and by increased BA reabsorption in the ileum via induction of the apical sodium-dependent BA transporter (Asbt). In contrast, metformin further worsened ethinylestradiol-induced impairment of bile secretion. This reduction was also BA dependent and corresponded with significant downregulation of Bsep, and Ntcp, major excretory and uptake transporters for BA in hepatocytes, respectively. The plasma concentrations of BA were consequently significantly increased in the metformin-treated mice. Altogether, our data indicate positive stimulation of bile secretion by metformin in the intact liver, but this drug also induces serious impairment of BA biliary secretion, with a marked increase in plasma concentrations in estrogen-induced cholestasis. Our results imply that metformin should be used with caution in situations with hormone-dependent cholestasis, such as ICP.

Canagliflozin Facilitates Reverse Cholesterol Transport Through Activation of AMPK/ABC Transporter Pathway

BACKGROUND AND PURPOSE

Cholesterol is an essential lipid and its homeostasis is a major factor for many diseases, such as hyperlipidemia, atherosclerosis, diabetes, and obesity. Sodium-glucose cotransporter 2 (SGLT2) inhibitor canagliflozin (Cana) is a new kind of hypoglycemic agent, which decreases urinary glucose reabsorption and reduces hyperglycemia. Cana has been shown to regulate serum lipid, decrease serum triglyceride and increase serum high-density lipoprotein-cholesterol (HDL-C), and improve cardiovascular outcomes. But evidence of how Cana impacted the cholesterol metabolism remains elusive.

METHODS

We treated Cana on mice with chow diet or western diet and then detected cholesterol metabolism in the liver and intestine. To explore the mechanism, we also treated hepG2 cells and Caco2 cells with different concentrations of Cana.

RESULTS

In this study, we showed that Cana facilitated hepatic and intestinal cholesterol efflux. Mechanically, Cana via activating adenosine monophosphate-activated protein kinase (AMPK) increased the expression of ATP-binding cassette (ABC) transporters ABCG5 and ABCG8 in liver and intestine, increased biliary and fecal cholesterol excretion.

CONCLUSION

This research confirms that Cana regulates cholesterol efflux and improves blood and hepatic lipid; this may be a partial reason for improving cardiovascular disease.

Obesity and aging: Molecular mechanisms and therapeutic approaches

The epidemic of obesity is a major challenge for health policymakers due to its far-reaching effects on population health and potentially overwhelming financial burden on healthcare systems. Obesity is associated with an increased risk of developing acute and chronic diseases, including hypertension, stroke, myocardial infarction, cardiovascular disease, diabetes, and cancer. Interestingly, the metabolic dysregulation associated with obesity is similar to that observed in normal aging, and substantial evidence suggests the potential of obesity to accelerate aging. Therefore, understanding the mechanism of fat tissue dysfunction in obesity could provide insights into the processes that contribute to the metabolic dysfunction associated with the aging process. Here, we review the molecular and cellular mechanisms underlying both obesity and aging, and how obesity and aging can predispose individuals to chronic health complications. The potential of lifestyle and pharmacological interventions to counter obesity and obesity-related pathologies, as well as aging, is also addressed.

Farnesoid X receptor via Notch1 directs asymmetric cell division of Sox9+ cells to prevent the development of liver cancer in a mouse model

Background

Asymmetrical cell division (ACD) maintains the proper number of stem cells to ensure self-renewal. The rate of symmetric division increases as more cancer stem cells (CSCs) become malignant; however, the signaling pathway network involved in CSC division remains elusive. FXR (Farnesoid X receptor), a ligand-activated transcription factor, has several anti-tumor effects and has been shown to target CSCs. Here, we aimed at evaluating the role of FXR in the regulation of the cell division of CSCs.

Methods

The FXR target gene and downstream molecular mechanisms were confirmed by qRT-PCR, Western blot, luciferase reporter assay, EMAS, Chip, and IF analyses. Pulse-chase BrdU labeling and paired-cell experiments were used to detect the cell division of liver CSCs. Gain- and loss-of-function experiments in Huh7 cells and mouse models were performed to support findings and elucidate the function and underlying mechanisms of FXR-Notch1 in liver CSC division.

Results

We demonstrated that activation of Notch1 was significantly elevated in the livers of hepatocellular carcinoma (HCC) in Farnesoid X receptor-knockout (FXR-KO) mice and that FXR expression negatively correlated with Notch1 level during chronic liver injury. Activation of FXR induced the asymmetric divisions of Sox9⁺ liver CSCs and ameliorated liver injury. Mechanistically, FXR directs Sox9⁺ liver CSCs from symmetry to asymmetry via inhibition of Notch1 expression and activity. Deletion of FXR signaling or over-expression of Notch1 greatly increased Notch1 expression and activity along with ACD reduction. FXR inhibited Notch1 expression by directly binding to its promoter FXRE. FXR also positively regulated Numb expression, contributing to a feedback circuit, which decreased Notch1 activity and directed ACD.

Conclusion

Our findings suggest that FXR represses Notch1 expression and directs ACD of Sox9⁺ cells to prevent the development of liver cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02298-6.

FXR in liver physiology: Multiple faces to regulate liver metabolism

The liver is the central metabolic hub which coordinates nutritional inputs and metabolic outputs. Food intake releases bile acids which can be sensed by the bile acid receptor FXR in the liver and the intestine. Hepatic and intestinal FXR coordinately regulate postprandial nutrient disposal in a network of interacting metabolic nuclear receptors. In this review we summarize and update the "classical roles" of FXR as a central integrator of the feeding state response, which orchestrates the metabolic processing of carbohydrates, lipids, proteins and bile acids. We also discuss more recent and less well studied FXR effects on amino acid, protein metabolism, autophagic turnover and inflammation. In addition, we summarize the recent understanding of how FXR signaling is affected by posttranslational modifications and by different FXR isoforms. These modifications and variations in FXR signaling might be considered when FXR is targeted pharmaceutically in clinical applications.

Effects of metformin on lipopolysaccharide induced inflammation by activating fibroblast growth factor 21

Lipopolysaccharide (LPS) is a component of the cell wall of Gram-negative bacteria that produces endotoxemia, which may cause septic shock. Metformin (MET) is a widely used hypoglycemic drug that exhibits anti-inflammatory properties. Fibroblast growth factor 21 (FGF21) is an endocrine polypeptide that affects glucose and lipid metabolism, and also possesses anti-inflammatory properties. We investigated the effects of MET and FGF21 on inflammation due to LPS induced endotoxemia in male rats. Animals were divided into five groups: control, LPS, pre-MET LPS, LPS + 1 h MET and LPS + 3 h MET. Serum levels of alanine aminotransferase, aspartate aminotransferase, FGF2, interleukin-10 and tumor necrosis factor alpha were measured. Malondialdehyde, myeloperoxidase and FGF21 levels were measured in liver tissue samples. Histopathology of all groups was assessed using hematoxylin and eosin stained sections. LPS caused severe inflammatory liver damage. MET exhibited a partially protective effect and reduced inflammation significantly. FGF21 is produced in the liver following inflammation and MET may increase its production.

Resveratrol Reduces COMPopathy in Mice Through Activation of Autophagy

Misfolding mutations in cartilage oligomeric matrix protein (COMP) cause it to be retained within the endoplasmic reticulum (ER) of chondrocytes, stimulating a multitude of damaging cellular responses including ER stress, inflammation, and oxidative stress, which ultimately culminates in the death of growth plate chondrocytes and pseudoachondroplasia (PSACH). Previously, we demonstrated that an antioxidant, resveratrol, substantially reduces the intracellular accumulation of mutant-COMP, dampens cellular stress, and lowers the level of growth plate chondrocyte death. In addition, we showed that resveratrol reduces mammalian target of rapamycin complex 1 (mTORC1) signaling, suggesting a potential mechanism. In this work, we investigate the role of autophagy in treatment of COMPopathies. In cultured chondrocytes expressing wild-type COMP or mutant-COMP, resveratrol significantly increased the number of Microtubule-associated protein 1A/1B-light chain 3 (LC3) vesicles, directly demonstrating that resveratrol-stimulated autophagy is an important component of the resveratrol-driven mechanism responsible for the degradation of mutant-COMP. Moreover, pharmacological inhibitors of autophagy suppressed degradation of mutant-COMP in our established mouse model of PSACH. In contrast, blockage of the proteasome did not substantially alter resveratrol clearance of mutant-COMP from growth plate chondrocytes. Mechanistically, resveratrol increased SIRT1 and PP2A expression and reduced MID1 expression and activation of phosphorylated protein kinase B (pAKT) and mTORC1 signaling in growth plate chondrocytes, allowing clearance of mutant-COMP by autophagy. Importantly, we show that optimal reduction in growth plate pathology, including decreased mutant-COMP retention, decreased mTORC1 signaling, and restoration of chondrocyte proliferation was attained when treatment was initiated between birth to 1 week of age in MT-COMP mice, translating to birth to approximately 2 years of age in children with PSACH. These results clearly demonstrate that resveratrol stimulates clearance of mutant-COMP by an autophagy-centric mechanism. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Post-Translational Modifications of FXR; Implications for Cholestasis and Obesity-Related Disorders

The Farnesoid X receptor (FXR) is a nuclear receptor which is activated by bile acids. Bile acids function in solubilization of dietary fats and vitamins in the intestine. In addition, bile acids have been increasingly recognized to act as signaling molecules involved in energy metabolism pathways, amongst others via activating FXR. Upon activation by bile acids, FXR controls the expression of many genes involved in bile acid, lipid, glucose and amino acid metabolism. An inability to properly use and store energy substrates may predispose to metabolic disorders, such as obesity, diabetes, cholestasis and non-alcoholic fatty liver disease. These diseases arise through a complex interplay between genetics, environment and nutrition. Due to its function in metabolism, FXR is an attractive treatment target for these disorders. The regulation of FXR expression and activity occurs both at the transcriptional and at the post-transcriptional level. It has been shown that FXR can be phosphorylated, SUMOylated and acetylated, amongst other modifications, and that these modifications have functional consequences for DNA and ligand binding, heterodimerization and subcellular localization of FXR. In addition, these post-translational modifications may selectively increase or decrease transcription of certain target genes. In this review, we provide an overview of the posttranslational modifications of FXR and discuss their potential involvement in cholestatic and metabolic disorders.

Restoration of mRNA Expression of Solute Carrier Proteins in Liver of Diet-Induced Obese Mice by Metformin

Metformin (MET), the most common medicine for type 2 diabetes (T2DM), improves insulin sensitivity by targeting the liver, intestine and other organs. Its impact on expression of the solute carrier (Slc) transporter genes have not been reported in the mechanism of insulin sensitization. In this study, we examined Slc gene expression in the liver and colon of diet-induced obese (DIO) mice treated with MET by transcriptomic analysis. There were 939 differentially expressed genes (DEGs) in the liver of DIO mice vs lean mice, which included 34 Slc genes. MET altered 489 DEGs in the liver of DIO mice, in which 23 were Slc genes. Expression of 20 MET-responsive Slc DEGs was confirmed by qRT-PCR, in which 15 Slc genes were altered in DIO mice and their expressions were restored by MET, including Slc2a10, Slc2a13, Slc5a9, Slc6a14, Slc7a9, Slc9a2, Slc9a3, Slc13a2, Slc15a2, Slc26a3, Slc34a2, Slc37a1, Slc44a4, Slc51b and Slc52a3. While, there were only 97 DEGs in the colon of DIO mice with 5 Slc genes, whose expression was not restored by MET. The data suggest that more genes were altered in the liver over the colon by the high fat diet (HFD). There were 20 Slc genes with alteration confirmed in the liver of DIO mice and 15 of them were restored by MET, which was associated with improvement of insulin sensitivity and obesity. The restoration may improve the uptake of glucose, amino acids, mannose, fructose, 1,5-anhydro-D-glucitol and bumetanide in hepatocytes of the liver of DIO mice. The study provides new insight into the mechanism of metformin action in insulin sensitization and obesity.

Constitutive Androstane Receptor-Mediated Inhibition of Metformin on Phase II Metabolic Enzyme SULT2A1

BACKGROUND

Metformin, as a first-line treatment for diabetes, interacts with many protein kinases and transcription factors which affect the expression of downstream target genes governing drug metabolism. Sulfotransferase, SULT2A1, one phase II metabolic enzyme, sulfonates both xenobiotic and endobiotic compounds to accelerate drug excretion. Herein, we designed experiments to investigate the effects and mechanisms of metformin on SULT2A1 expression in vitro.

METHODS

The hepatocellular carcinoma cell line, HepaRG, was cultured with different concentrations of metformin. The cell viability was measured using CCK8 kit. HepaRG was used to evaluate the protein expression of pregnane X receptor (PXR), the constitutive androstane receptor (CAR), SULT2A1, AMP-activated protein kinase (AMPK), and phosphorylation of AMPK (p-AMPK), respectively, at different concentrations of metformin with or without rifampin (human PXR activator) and CITCO (human CAR activator). The coregulators with CAR on SULT2A1 promoter response elements have also been characterized.

RESULTS

We showed that metformin did not affect the basic expression of SULT2A1 but could suppress the expression of SULT2A1 induced by the activator of human CAR. Investigations revealed that metformin which could block CAR nuclear translocation further suppress SULT2A1. In addition, we found that the prevented CAR transfer into the nucleus by metformin was partially an AMPK-dependent event.

CONCLUSION

The present study indicated that the activation of AMPK-CAR pathway mediated the suppression of SULT2A1 by metformin. Metformin may affect the metabolism and clearance of drugs which are SULT2A1 substrates. The results that emerged from this work provide substantial insights into an appropriate medication in the treatment of diabetes patients.

Glibenclamide, ATP and metformin increases the expression of human bile salt export pump ABCB11

Background: Bile salt export pump (BSEP/ABCB11) is important in the maintenance of the enterohepatic circulation of bile acids and drugs. Drugs such as rifampicin and glibenclamide inhibit BSEP. Progressive familial intrahepatic cholestasis type-2, a lethal pediatric disease, some forms of intrahepatic cholestasis of pregnancy, and drug-induced cholestasis are associated with BSEP dysfunction. 

Methods: We started with a bioinformatic approach to identify the relationship between ABCB11 and other proteins, microRNAs, and drugs. A microarray data set of the liver samples from ABCB11 knockout mice was analyzed using GEO2R. Differentially expressed gene pathway enrichment analysis was conducted using ClueGo. A protein-protein interaction network was constructed using STRING application in Cytoscape. Networks were analyzed using Cytoscape. CyTargetLinker was used to screen the transcription factors, microRNAs and drugs. Predicted drugs were validated on human liver cell line, HepG2. BSEP expression was quantified by real-time PCR and western blotting.

Results:ABCB11 knockout in mice was associated with a predominant upregulation and downregulation of genes associated with cellular component movement and sterol metabolism, respectively. We further identified the hub genes in the network. Genes related to immune activity, cell signaling, and fatty acid metabolism were dysregulated.  We further identified drugs (glibenclamide and ATP) and a total of 14 microRNAs targeting the gene. Western blot and real-time PCR analysis confirmed the upregulation of BSEP on the treatment of HepG2 cells with glibenclamide, ATP, and metformin.

Conclusions: The differential expression of cell signaling genes and those related to immune activity in ABCB11 KO animals may be secondary to cell injury. We have found glibenclamide, ATP, and metformin upregulates BSEP. The mechanisms involved and the clinical relevance of these findings need to be investigated.

Picroside II alleviates liver injury induced by alpha-naphthylisothiocyanate through AMPK-FXR pathway

Alpha-naphthylisothiocyanate (ANIT) is a typical hepatotoxicant that causes cholestasis, which causes toxic bile acid accumulation in the liver and leads to liver injury. Picroside II (PIC), one of the dominant effective components extracted from Picrorhiza scrophulariiflora Pennell, exhibits many pharmacological effects. However, the role of AMP-activated protein kinase (AMPK)-Farnesoid X receptor (FXR) pathway in the hepatoprotective effect of PIC against ANIT-induced cholestasis remains largely unknown. This study aimed to investigate the mechanisms of PIC on ANIT-induced cholestasis in vivo and in vitro. Our results showed that PIC protected against ANIT-induced liver injury in primary mouse hepatocytes, and decreased serum biochemical markers and lessened histological injuries in mice. ANIT inhibited FXR and its target genes of bile acid synthesis enzymes sterol-12α-hydroxylase (CYP8B1), and increase bile acid uptake transporter Na + -dependent taurocholate transporter (NTCP), efflux transporter bile salt export pump (BSEP) and bile acid metabolizing enzymes UDP-glucuronosyltransferase 1a1 (UGT1A1) expressions. PIC prevented its downregulation of FXR, NTCP, BSEP and UGT1A1, and further reduced CYP8B1 by ANIT. Furthermore, ANIT activated AMPK via ERK1/2-LKB1 pathway. PIC inhibited ERK1/2, LKB1 and AMPK phosphorylation in ANIT-induced cholestasis in vivo and in vitro. AICAR, an AMPK agonist, blocked PIC-mediated changes in FXR, CYP8B1 and BSEP expression in vitro. Meanwhile, U0126, an ERK1/2 inhibitor, further repressed ERK1/2-LKB1-AMPK pathway phosphorylation. In conclusion, PIC regulated bile acid-related transporters and enzymes to protect against ANIT-induced liver injury, which related to ERK1/2-LKB1-AMPK pathway. Thus, this study extends the understanding of the anti-cholestasis effect of PIC and provides new therapeutic targets for cholestasis treatment.

Regulation of autophagy by bile acids and in cholestasis - CholestoPHAGY or CholeSTOPagy

Autophagy is a lysosomal degradation pathway in which the cell self-digests its own components to provide nutrients in harsh environmental conditions. It also represents an opportunity to rid the cell of superfluous and damaged organelles, misfolded proteins or invaded microorganisms. Liver autophagy contributes to basic hepatic functions such as lipid, glycogen and protein turnover. Deregulated hepatic autophagy has been linked to many liver diseases including alpha-1-antitrypsin deficiency, alcoholic and non-alcoholic fatty liver diseases, hepatitis B and C infections, liver fibrosis as well as liver cancer. Recently, bile acids and the bile acid receptor FXR have been implicated in the regulation of hepatic autophagy, which implies a role of autophagy also for cholestatic liver diseases. This review summarizes the current evidence of bile acid mediated effects on autophagy and how this affects cholestatic liver diseases. Although detailed studies are lacking, we suggest a concept that the activity of autophagy in cholestasis depends on the disease stage, where autophagy may be induced at early stages ("cholestophagy") but may be impaired in prolonged cholestatic states ("cholestopagy").

Comparative analysis of fecal metabolite profiles in HFD-induced obese mice after oral administration of huangjinya green tea extract

To explore the impact of Huangjinya on metabolic disorders and host endogenous metabolite profiles, high-fat diet (HFD)-fed mice were administrated with Huangjinya green tea extract (HGT) at the dose of 150 or 300 mg/kg for 9 weeks. Epigallocatechin gallate was the main catechin derivative, followed by epigallocatechin and catechin presented in HGT, which contained high levels of free amino acids (50.30 ± 0.60 mg/g). HGT significantly alleviated glucose and insulin intolerance, reduced hepatic lipid accumulation and liver steatosis, and prevented white adipose tissue expansion in HFD-fed mice. Untargeted mass spectrometry-based metabolomics analysis revealed that HGT reduced the abundance of fecal branched-chain amino acids, aromatic amino acids, sphingolipids, and most acyl cholines, modulated bile acid metabolism by increasing chenodeoxycholate and reducing cholic acid content, and increased unsaturated fatty acids content. Fatherly, HGT activated insulin/PI3K/Akt and AMPK signaling pathways in the liver, reduced adipogenic and lipogenic genes expression, and promoted the genes expression related to lipolysis and adipocyte browning in white adipose tissue, contributed to improving metabolic syndrome in HFD-fed mice. The current study reported the impact of HGT supplementation on endogenous metabolite profiles, and highlights the positive roles of HGT in preventing diet-induced obesity and the related metabolic disorders.

Metabolomics reveals the toxicological effects of polar compounds from frying palm oil

Polar compounds from frying oils have been found to be harmful to health. However, the mechanisms underlying this phenomenon have largely remained elusive. In this study, mass spectrometry-based metabolomics was used to investigate the toxicological effects of polar compounds. The serum and hepatic metabolites from polar compound-treated mice were measured using liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry. Multi-variate statistical analysis showed that a total of 36 serum metabolites and 18 hepatic metabolites were altered in the polar compound-treated mice as compared with that for normal diet-fed animals. These metabolic changes suggested novel alterations in lipid metabolism with the increase in phospholipids, fatty acids, and cholesterol and the decrease in choline, betaine and l-acetylcarnitine. The TCA cycle and carbohydrate, amino acid and purine metabolism were also impaired, with a significant elevation of d-glucose, d-maltose, β-mannobiose, branched chain amino acids, aromatic amino acids, and uric acid and a decline in succinate, serine, aspartate, arginine and ornithine. Pearson correlation analysis demonstrated the strong correlations between specific metabolic alterations and the redox index. Our overall findings reveal that polar compounds may progressively cause lipid deposition, impaired energy metabolism and oxidative stress, resulting in toxicological effects on the mammalian health.

Metformin Preconditioning Improves Hepatobiliary Function and Reduces Injury in a Rat Model of Normothermic Machine Perfusion and Orthotopic Transplantation

Background.

Preconditioning of donor livers before organ retrieval may improve organ quality after transplantation. We investigated whether preconditioning with metformin reduces preservation injury and improves hepatobiliary function in rat donor livers during ex situ normothermic machine perfusion (NMP) and after orthotopic liver transplantation.

Methods.

Lewis rats were administered metformin via oral gavage, after which a donor hepatectomy was performed followed by a standardized cold storage period of 4 hours. Graft assessment was performed using NMP via double perfusion of the hepatic artery and portal vein. In an additional experiment, rat donor livers preconditioned with metformin were stored on ice for 4 hours and transplanted to confirm postoperative liver function and survival. Data were analyzed and compared with sham-fed controls.

Results.

Graft assessment using NMP confirmed that preconditioning significantly improved ATP production, markers for hepatobiliary function (total bile production, biliary bilirubin, and bicarbonate), and significantly lowered levels of lactate, glucose, and apoptosis. After orthotopic liver transplantation, metformin preconditioning significantly reduced transaminase levels.

Conclusions.

Preconditioning with metformin lowers hepatobiliary injury and improves hepatobiliary function in an in situ and ex situ model of rat donor liver transplantation.

Molecular Physiology of Bile Acid Signaling in Health, Disease, and Aging

Over the past two decades, bile acids (BAs) have become established as important signaling molecules that enable fine-tuned inter-tissue communication from the liver, their site of production, over the intestine, where they are modified by the gut microbiota, to virtually any organ, where they exert their pleiotropic physiological effects. The chemical variety of BAs, to a large extent determined by the gut microbiome, also allows for a complex fine-tuning of adaptive responses in our body. This review provides an overview of the mechanisms by which BA receptors coordinate several aspects of physiology and highlights new therapeutic strategies for diseases underlying pathological BA signaling.

Metformin ameliorates bile duct ligation-induced acute hepatic injury via regulation of ER stress

Cholestasis is a condition in which the bile duct becomes narrowed or clogged by a variety of factors and bile acid is not released smoothly. Bile acid-induced liver injury is facilitated by necrotic cell death, neutrophil infiltration, and inflammation. Metformin, the first-line treatment for type 2 diabetes, is known to reduce not only blood glucose but also inflammatory responses. In this study, we investigated the effects of metformin on liver injury caused by cholestasis with bile acid-induced hepatocyte injury. Static bile acid-induced liver injury is thought to be related to endoplasmic reticulum (ER) stress, inflammatory response, and chemokine expression. Metformin treatment reduced liver injury caused by bile acid, and it suppressed ER stress, inflammation, chemokine expression, and neutrophil infiltration. Similar results were obtained in mouse primary hepatocytes exposed to bile acid. Hepatocytes treated with tauroursodeoxycholic acid, an ER stress inhibitor, showed inhibition of ER stress, as well as reduced levels of inflammation and cell death. These results suggest that metformin may protect against liver injury by suppressing ER stress and inflammation and reducing chemokine expression.

Discovery, Structural Refinement and Therapeutic Potential of Farnesoid X Receptor Activators

Farnesoid X receptor acts as bile acid sensing transcription factor and has been identified as valuable molecular drug target to treat severe liver disorders, such as non-alcoholic steatohepatitis (NASH). Preclinical and clinical data indicate anti-fibrotic effects obtained with FXR activation that also appear promising for other fibrotic diseases beyond NASH. Strong efforts in FXR ligand discovery have yielded potent steroidal and non-steroidal FXR activators, some of which have been studied in clinical trials. While the structure–activity relationship of some FXR agonist frameworks have been studied extensively, the structural diversity of potent FXR activator chemotypes is still limited to a handful of well-studied compound classes. Together with safety concerns related to full therapeutic activation of FXR, this indicates the need for novel innovative FXR ligands with selective modulatory properties. This chapter evaluates FXR's value as drug target with emphasis on fibrotic diseases, analyses FXR ligand recognition and requirements and focuses on the discovery and structural refinement of leading FXR activator chemotypes.