Antiatherosclerotic effect of farnesoid X receptor

Obeticholic acid's effect on HDL function in MASH varies by diabetic status

Inflammation and oxidative stress are the key factors in the pathogenesis of both metabolic dysfunction-associated steatohepatitis (MASH) and atherosclerosis. Obeticholic acid (OCA), a farnesoid X receptor (FXR) agonist, improves hepatic inflammation and fibrosis in patients with MASH. However, it also reduces HDL cholesterol, suggesting that OCA may increase cardiovascular disease (CVD) risk in patients with MASH. We assessed HDL cholesterol efflux function, antioxidant (paraoxonase and ceruloplasmin activity), pro-inflammatory index, and particle sizes in a small group of patients with and without diabetes (n = 10/group) at baseline and after 18 months of OCA treatment. Patients on lipid-lowering medications (statins, fibrates) were excluded. At baseline, ferritin levels were higher in patients with MASH without diabetes (336.5 [157.0, 451.0] vs. 83 [36.0, 151.0] ng/mL, p < 0.005). Markers of HDL functions were similar in both groups. OCA therapy significantly improved liver histology and liver enzymes but increased alkaline phosphatase levels in nondiabetic patients with MASH (p < 0.05). However, it did not have any significant effect on cholesterol efflux and the antioxidant paraoxonase functions. In nondiabetics, ceruloplasmin (CP) antioxidant activity decreased (p < 0.005) and the pro-inflammatory index of HDL increased (p < 0.005) due to OCA therapy. In contrast, in diabetics, OCA increased levels of pre-β-HDL-the HDL particles enhanced protective capacity (p = 0.005) with no alteration in HDL functionality. In all patients, serum glucose levels were negatively correlated with OCA-induced change in pro-inflammatory function in HDL (p < 0.001), which was primarily due to diabetes (p = 0.05). These preliminary results suggest a distinct effect of OCA therapy on diabetic and nondiabetic patients with MASH and warrant a future large-scale study.

Sex differences in lipidomic and bile acid plasma profiles in patients with and without coronary artery disease

BACKGROUND

Lipids, including phospholipids and bile acids, exert various signaling effects and are thought to contribute to the development of coronary artery disease (CAD). Here, we aimed to compare lipidomic and bile acid profiles in the blood of patients with and without CAD stratified by sex.

METHODS

From 2015 to 2022, 3,012 patients who underwent coronary angiography were recruited in the INTERCATH cohort. From the overall cohort, subgroups were defined using patient characteristics such as CAD vs. no CAD, 1st vs. 3rd tertile of LDL-c, and female vs. male sex. Hereafter, a matching algorithm based on age, BMI, hypertension status, diabetes mellitus status, smoking status, the Mediterranean diet score, and the intake of statins, triglycerides, HDL-c and hs-CRP in a 1:1 ratio was implemented. Lipidomic analyses of stored blood samples using the Lipidyzer platform (SCIEX) and bile acid analysis using liquid chromatography with tandem mass spectrometry (LC‒MS/MS) were carried out.

RESULTS

A total of 177 matched individuals were analyzed; the median ages were 73.5 years (25th and 75th percentile: 64.1, 78.2) and 71.9 years (65.7, 77.2) for females and males with CAD, respectively, and 67.6 years (58.3, 75.3) and 69.2 years (59.8, 76.8) for females and males without CAD, respectively. Further baseline characteristics, including cardiovascular risk factors, were balanced between the groups. Women with CAD had decreased levels of phosphatidylcholine and diacylglycerol, while no differences in bile acid profiles were detected in comparison to those of female patients without CAD. In contrast, in male patients with CAD, decreased concentrations of the secondary bile acid species glycolithocholic and lithocholic acid, as well as altered levels of specific lipids, were detected compared to those in males without CAD. Notably, male patients with low LDL-c and CAD had significantly greater concentrations of various phospholipid species, particularly plasmalogens, compared to those in high LDL-c subgroup.

CONCLUSIONS

We present hypothesis-generating data on sex-specific lipidomic patterns and bile acid profiles in CAD patients. The data suggest that altered lipid and bile acid composition might contribute to CAD development and/or progression, helping to understand the different disease trajectories of CAD in women and men.

REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT04936438 , Unique identifier: NCT04936438.

Mechanism of Bile Acid in Regulating Platelet Function and Thrombotic Diseases

Platelets play a key role in physiological hemostasis and pathological thrombosis. Based on the limitations of current antiplatelet drugs, it's important to elucidate the mechanisms of regulating platelet activation. In addition to dissolving lipid nutrients, bile acids (BAs) can regulate platelet function. However, the specific mechanisms underlying BAs-mediated effects on platelet activation and thrombotic diseases remain unknown. Therefore, the effects of BAs on platelets and intracellular regulatory mechanisms are explored. It is showed that the inhibitory effect of secondary BAs is more significant than that of primary BAs; lithocholic acid (LCA) shows the highest inhibitory effect. In the process of platelet activation, BAs suppress platelet activation via the spleen tyrosine kinase (SYK), protein kinase B (Akt), and extracellular signal-regulated kinase1/2 (Erk1/2) pathways. Nck adaptor proteins (NCK1) deficiency significantly suppress the activity of platelets and arterial thrombosis. Phosphorylated proteomics reveal that LCA inhibited phosphorylation of syntaxin-11 at S80/81 in platelets. Additional LCA supplementation attenuated atherosclerotic plaque development and reduced the inflammation in mice. In conclusion, BAs play key roles in platelet activation via Syk, Akt, ERK1/2, and syntaxin-11 pathways, which are associated with NCK1. The anti-platelet effects of BAs provide a theoretical basis for the prevention and therapy of thrombotic diseases.

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.

Suppression of Lung Oxidative Stress, Inflammation, and Fibrosis following Nitrogen Mustard Exposure by the Selective Farnesoid X Receptor Agonist Obeticholic Acid

Nitrogen mustard (NM) is a cytotoxic vesicant known to cause pulmonary injury that can progress to fibrosis. NM toxicity is associated with an influx of inflammatory macrophages in the lung. Farnesoid X receptor (FXR) is a nuclear receptor involved in bile acid and lipid homeostasis that has anti-inflammatory activity. In these studies, we analyzed the effects of FXR activation on lung injury, oxidative stress, and fibrosis induced by NM. Male Wistar rats were exposed to phosphate-buffered saline (vehicle control) or NM (0.125 mg/kg) by intratracheal Penncentury-MicroSprayer aerosolization; this was followed by treatment with the FXR synthetic agonist, obeticholic acid (OCA, 15 mg/kg), or vehicle control (0.13-0.18 g peanut butter) 2 hours later and then once per day, 5 days per week thereafter for 28 days. NM caused histopathological changes in the lung, including epithelial thickening, alveolar circularization, and pulmonary edema. Picrosirius red staining and lung hydroxyproline content were increased, indicative of fibrosis; foamy lipid-laden macrophages were also identified in the lung. This was associated with aberrations in pulmonary function, including increases in resistance and hysteresis. Following NM exposure, lung expression of HO-1 and iNOS, and the ratio of nitrates/nitrites in bronchoalveolar lavage fluid (BAL), markers of oxidative stress increased, along with BAL levels of inflammatory proteins, fibrinogen, and sRAGE. Administration of OCA attenuated NM-induced histopathology, oxidative stress, inflammation, and altered lung function. These findings demonstrate that FXR plays a role in limiting NM-induced lung injury and chronic disease, suggesting that activating FXR may represent an effective approach to limiting NM-induced toxicity. SIGNIFICANCE STATEMENT: In this study, the role of farnesoid-X-receptor (FXR) in mustard vesicant-induced pulmonary toxicity was analyzed using nitrogen mustard (NM) as a model. This study's findings that administration of obeticholic acid, an FXR agonist, to rats reduces NM-induced pulmonary injury, oxidative stress, and fibrosis provide novel mechanistic insights into vesicant toxicity, which may be useful in the development of efficacious therapeutics.

Defective Bile Acid Signaling Promotes Vascular Dysfunction, Supporting a Role for G-Protein Bile Acid Receptor 1/Farnesoid X Receptor Agonism and Statins in the Treatment of Nonalcoholic Fatty Liver Disease

BACKGROUND

Patients with nonalcoholic fatty liver disease are at increased risk to develop atherosclerotic cardiovascular diseases. FXR and GPBAR1 are 2 bile acid-activated receptors exploited in the treatment of nonalcoholic fatty liver disease: whether dual GPBAR1/FXR agonists synergize with statins in the treatment of the liver and cardiovascular components of nonalcoholic fatty liver disease is unknown.

METHODS AND RESULTS

Investigations of human aortic samples obtained from patients who underwent surgery for aortic aneurysms and Gpbar1-/-, Fxr-/-, and dual Gpbar1-/-Fxr-/- mice demonstrated that GPBAR1 and FXR are expressed in the aortic wall and regulate endothelial cell/macrophage interactions. The expression of GPBAR1 in the human endothelium correlated with the expression of inflammatory biomarkers. Mice lacking Fxr and Gpbar1-/-/Fxr-/- display hypotension and aortic inflammation, along with altered intestinal permeability that deteriorates with age, and severe dysbiosis, along with dysregulated bile acid synthesis. Vasomotor activities of aortic rings were altered by Gpbar1 and Fxr gene ablation. In apolipoprotein E-/- and wild-type mice, BAR502, a dual GPBAR1/FXR agonist, alone or in combination with atorvastatin, reduced cholesterol and low-density lipoprotein plasma levels, mitigated the development of liver steatosis and aortic plaque formation, and shifted the polarization of circulating leukocytes toward an anti-inflammatory phenotype. BAR502/atorvastatin reversed intestinal dysbiosis and dysregulated bile acid synthesis, promoting a shift of bile acid pool composition toward FXR antagonists and GPBAR1 agonists.

CONCLUSIONS

FXR and GPBAR1 maintain intestinal, liver, and cardiovascular homeostasis, and their therapeutic targeting with a dual GPBAR1/FXR ligand and atorvastatin holds potential in the treatment of liver and cardiovascular components of nonalcoholic fatty liver disease.

Activation of GPBAR1 attenuates vascular inflammation and atherosclerosis in a mouse model of NAFLD-related cardiovascular disease

While patients with nonalcoholic fatty liver disease (NAFLD) are at increased risk to develop clinically meaningful cardiovascular diseases (CVD), there are no approved drug designed to target the liver and CVD component of NAFLD. GPBAR1, also known as TGR5, is a G protein coupled receptor for secondary bile acids. In this study we have investigated the effect of GPBAR1 activation by BAR501, a selective GPBAR1 agonist, in Apolipoprotein E deficient (ApoE-/-) mice fed a high fat diet and fructose (Western diet), a validated model of NAFLD-associated atherosclerosis. Using aortic samples from patients who underwent surgery for abdominal aneurism, and ex vivo experiments with endothelial cells and human macrophages, we were able to co-localize the expression of GPBAR1 in CD14+ and PECAM1+ cells. Similar findings were observed in the aortic plaques from ApoE-/- mice. Treating ApoE-/- mice with BAR501, 30 mg/kg for 14 weeks, attenuated the body weight gain while ameliorated the insulin sensitivity by increasing the plasma concentrations of GLP-1 and FGF15. Activation of GPBAR1 reduced the aorta thickness and severity of atherosclerotic lesions and decreased the amount of plaques macrophages. Treating ApoE-/- mice reshaped the aortic transcriptome promoting the expression of anti-inflammatory genes, including IL-10, as also confirmed by tSNE analysis of spleen-derived macrophages. Feeding ApoE-/- mice with BAR501 redirected the bile acid synthesis and the composition of the intestinal microbiota. In conclusion, GPBAR1 agonism attenuates systemic inflammation and improve metabolic profile in a genetic/dietetic model of atherosclerosis. BAR501 might be of utility in the treatment for NAFLD-related CVD.

Bile Acid Network and Vascular Calcification-Associated Diseases: Unraveling the Intricate Connections and Therapeutic Potential

Bile acids play a crucial role in promoting intestinal nutrient absorption and biliary cholesterol excretion, thereby protecting the liver from cholesterol accumulation and bile acid toxicity. Additionally, bile acids can bind to specific nuclear and membrane receptors to regulate energy expenditure and specific functions of particular tissues. Vascular calcification refers to the pathological process of calcium-phosphate deposition in blood vessel walls, which serves as an independent predictor for cardiovascular adverse events. In addition to aging, this pathological change is associated with aging-related diseases such as atherosclerosis, hypertension, chronic kidney disease, diabetes mellitus, and osteoporosis. Emerging evidence suggests a close association between the bile acid network and these aforementioned vascular calcification-associated conditions. Several bile acids have been proven to participate in calcium-phosphate metabolism, affecting the transdifferentiation of vascular smooth muscle cells and thus influencing vascular calcification. Targeting the bile acid network shows potential for ameliorating these diseases and their concomitant vascular calcification by regulating pathways such as energy metabolism, inflammatory response, oxidative stress, and cell differentiation. Here, we present a summary of the metabolism and functions of the bile acid network and aim to provide insights into the current research on the profound connections between the bile acid network and these vascular calcification-associated diseases, as well as the therapeutic potential.

Impact of intestinal microenvironments in obesity and bariatric surgery on shaping macrophages

Obesity is associated with alterations in tissue composition, systemic cellular metabolism, and low-grade chronic inflammation. Macrophages are heterogenous innate immune cells ubiquitously localized throughout the body and are key components of tissue homeostasis, inflammation, wound healing, and various disease states. Macrophages are highly plastic and can switch their phenotypic polarization and change function in response to their local environments. Here, we discuss how obesity alters the intestinal microenvironment and potential key factors that can influence intestinal macrophages as well as macrophages in other organs, including adipose tissue and hematopoietic organs. As bariatric surgery can induce metabolic adaptation systemically, we discuss the potential mechanisms through which bariatric surgery reshapes macrophages in obesity.

The interplay between microbial metabolites and macrophages in cardiovascular diseases: A comprehensive review

The gut microbiome has emerged as a crucial player in developing and progressing cardiovascular diseases (CVDs). Recent studies have highlighted the role of microbial metabolites in modulating immune cell function and their impact on CVD. Macrophages, which have a significant function in the pathogenesis of CVD, are very vulnerable to the effects of microbial metabolites. Microbial metabolites, such as short-chain fatty acids (SCFAs) and trimethylamine-N-oxide (TMAO), have been linked to atherosclerosis and the regulation of immune functions. Butyrate has been demonstrated to reduce monocyte migration and inhibit monocyte attachment to injured endothelial cells, potentially contributing to the attenuation of the inflammatory response and the progression of atherosclerosis. On the other hand, TMAO, another compound generated by gut bacteria, has been linked to atherosclerosis due to its impact on lipid metabolism and the accumulation of cholesterol in macrophages. Indole-3-propionic acid, a tryptophan metabolite produced solely by microbes, has been found to promote the development of atherosclerosis by stimulating macrophage reverse cholesterol transport (RCT) and raising the expression of ABCA1. This review comprehensively discusses how various microbiota-produced metabolites affect macrophage polarization, inflammation, and foam cell formation in CVD. We also highlight the mechanisms underlying these effects and the potential therapeutic applications of targeting microbial metabolites in treating CVD.

Hepatoprotective effect of Typhaneoside on non-alcoholic fatty liver disease via farnesoid X receptor in vivo and in vitro

Non-alcoholic fatty liver disease (NAFLD) is one of the most frequent health issues. The improvement of NAFLD is related to the activation of the farnesoid X receptor (FXR). Typhaneoside (TYP) is the main component of Typha orientalis Presl, which plays a positive role in the resistance of glucose and lipid metabolism disorders. This study aims to investigate the alleviative effect and the underlying mechanism of TYP on OAPA-induced cells and high-fat-diet (HFD)-induced mice with disorders of glucose and lipid metabolism, inflammation, oxidative stress and lower thermogenesis through FXR signaling. All the serum lipid, body weight, oxidative stress and inflammatory levels of WT mice were significantly increased after HFD administration. These mice were presented with pathological injury, liver tissue attenuation, energy expenditure, insulin resistance, and impaired glucose tolerance. These above-mentioned changes in HFD-induced mice were remarkably reversed by TYP, which improved HFD-induced energy expenditure, oxidative stress, inflammation, insulin resistance, and lipid accumulation in a dose-dependent manner by activating the expression of FXR. Furthermore, using a high throughput drug screening strategy based on fluorescent reporter genes, we found that TYP functions as a natural agonist of FXR.TYP-mediated FXR activation also significantly repressed TG hyperaccumulation in mouse primary Hepatocytes (MPHs). However, these beneficial effects of TYP were not observed in FXR^-/- MPHs. Overall, activation of the FXR pathway by TYP is related to the improvement of metabolic parameters, such as blood glucose, lipid accumulation, insulin resistance, inflammation, oxidative stress and energy expenditure in vitro and in vivo.

Emerging Roles of Gut Microbial Modulation of Bile Acid Composition in the Etiology of Cardiovascular Diseases

Despite advances in preventive measures and treatment options, cardiovascular disease (CVD) remains the number one cause of death globally. Recent research has challenged the traditional risk factor profile and highlights the potential contribution of non-traditional factors in CVD, such as the gut microbiota and its metabolites. Disturbances in the gut microbiota have been repeatedly associated with CVD, including atherosclerosis and hypertension. Mechanistic studies support a causal role of microbiota-derived metabolites in disease development, such as short-chain fatty acids, trimethylamine-N-oxide, and bile acids, with the latter being elaborately discussed in this review. Bile acids represent a class of cholesterol derivatives that is essential for intestinal absorption of lipids and fat-soluble vitamins, plays an important role in cholesterol turnover and, as more recently discovered, acts as a group of signaling molecules that exerts hormonal functions throughout the body. Studies have shown mediating roles of bile acids in the control of lipid metabolism, immunity, and heart function. Consequently, a picture has emerged of bile acids acting as integrators and modulators of cardiometabolic pathways, highlighting their potential as therapeutic targets in CVD. In this review, we provide an overview of alterations in the gut microbiota and bile acid metabolism found in CVD patients, describe the molecular mechanisms through which bile acids may modulate CVD risk, and discuss potential bile-acid-based treatment strategies in relation to CVD.

Hepatic and renal improvements with FXR agonist vonafexor in individuals with suspected fibrotic NASH

BACKGROUND & AIMS

The LIVIFY trial investigated the safety, tolerability, and efficacy of vonafexor, a second-generation, non-bile acid farnesoid X receptor agonist in patients with suspected fibrotic non-alcoholic steatohepatitis (NASH).

METHODS

This double-blind phase IIa study was conducted in two parts. Patients were randomised (1:1:1:1) to receive placebo, vonafexor 100 mg twice daily (VONA-100BID), vonafexor 200 mg once daily (VONA-200QD), or 400 mg vonafexor QD (VONA-400QD) in Part A (safety run-in, pharmacokinetics/pharmacodynamics) or placebo, vonafexor 100 mg QD (VONA-100QD), or VONA-200QD (1:1:1) in Part B. The primary efficacy endpoint was a reduction in liver fat content (LFC) by MRI-proton density fat fraction, while secondary endpoints included reduced corrected T1 values and liver enzymes, from baseline to Week 12.

RESULTS

One hundred and twenty patients were randomised (Part A, n = 24; Part B, n = 96). In Part B, there was a significant reduction in least-square mean (SE) absolute change in LFC from baseline to Week 12 for VONA-100QD (-6.3% [0.9]) and VONA-200QD (-5.4% [0.9]), vs. placebo (-2.3% [0.9], p = 0.002 and 0.012, respectively). A >30% relative LFC reduction was achieved by 50.0% and 39.3% of patients in the VONA-100QD and VONA-200QD arms, respectively, but only in 12.5% in the placebo arm. Reductions in body weight, liver enzymes, and corrected T1 were also observed with vonafexor. Creatinine-based glomerular filtration rate improved in the active arms but not the placebo arm. Mild to moderate generalised pruritus was reported in 6.3%, 9.7%, and 18.2% of participants in the placebo, VONA-100QD, and VONA-200QD arms, respectively.

CONCLUSIONS

In patients with suspected fibrotic NASH, vonafexor was safe and induced potent liver fat reduction, improvement in liver enzymes, weight loss, and a possible renal benefit.

CLINICAL TRIAL NUMBER (EUDRACT)

2018-003119-22.

CLINICALTRIALS

GOV IDENTIFIER

NCT03812029.

IMPACT AND IMPLICATIONS

Non-alcoholic steatohepatitis (NASH) has become a leading cause of chronic liver disease worldwide. Affected patients are also at higher risk of developing chronic kidney disease. There are no approved therapies and only few options to treat this population. The phase IIa LIVIFY trial results show that single daily administration of oral vonafexor, an FXR agonist, leads in the short term to a reduction in liver fat, liver enzymes, fibrosis biomarkers, body weight and abdominal circumference, and a possible improvement in kidney function, while possible mild moderate pruritus (a peripheral FXR class effect) and an LDL-cholesterol increase are manageable with lower doses and statins. These results support exploration in longer and larger trials, with the aim of addressing the unmet medical need in NASH.

The role of the farnesoid X receptor in kidney health and disease: a potential therapeutic target in kidney diseases

The prevalence of kidney diseases has been increasing worldwide due to the aging population and has results in an increased socioeconomic burden as well as increased morbidity and mortality. A deep understanding of the mechanisms underlying the physiological regulation of the kidney and the pathogenesis of related diseases can help identify potential therapeutic targets. The farnesoid X receptor (FXR, NR1H4) is a primary nuclear bile acid receptor that transcriptionally regulates bile acid homeostasis as well as glucose and lipid metabolism in multiple tissues. The roles of FXR in tissues other than hepatic and intestinal tissues are poorly understood. In studies over the past decade, FXR has been demonstrated to have a protective effect against kidney diseases through its anti-inflammatory and antifibrotic effects; it also plays roles in glucose and lipid metabolism in the kidney. In this review, we discuss the physiological role of FXR in the kidney and its pathophysiological roles in various kidney diseases, including acute kidney injury and chronic kidney diseases, diabetic nephropathy, and kidney fibrosis. Therefore, the regulatory mechanisms involving nuclear receptors, such as FXR, in the physiology and pathophysiology of the kidney and the development of agonists and antagonists for modulating FXR expression and activation should be elucidated to identify therapeutic targets for the treatment of kidney diseases.

Gut microbiome and metabolites, the future direction of diagnosis and treatment of atherosclerosis?

Over the past few decades, the treatment of atherosclerotic cardiovascular disease has mainly been through an LDL lowering strategy and treatments targeting other traditional risk factors for atherosclerosis, which has significantly reduced cardiovascular mortality. However, the overall benefit of targeting these risk factors has stagnated, and the discovery of new therapeutic targets for atherosclerosis remains a challenge. Accumulating evidence from clinical and animal experiments has revealed that the gut microbiome play a significant role in human health and disease, including cardiovascular diseases. The gut microbiome contribute to host health and disease through microbial composition and function. The gut microbiome function like an endocrine organ by generating bioactive metabolites that can impact atherosclerosis. In this review, we describe two gut microbial metabolites/pathways by which the gut affects atherosclerotic cardiovascular disease. On the one hand, we discuss the effects of trimethylamine oxide (TMAO), bile acids and aromatic amino acid metabolites on the development of atherosclerosis, and the protective effects of beneficial metabolites short chain amino acids and polyamines on atherosclerosis. On the other hand, we discuss novel therapeutic strategies for directly targeting gut microbial metabolites to improve cardiovascular outcomes. Reducing gut-derived TMAO levels and interfering with the bile acid receptor farnesoid X receptor (FXR) are new therapeutic strategies for atherosclerotic disease. Enzymes and receptors in gut microbiota metabolic pathways are potential new drug targets. We need solid insight into these underlying mechanisms to pave the way for therapeutic strategies targeting gut microbial metabolites/pathways for atherosclerotic cardiovascular disease.

Role of gut microbe-derived metabolites in cardiometabolic diseases: Systems based approach

BACKGROUND

The gut microbiome influences host physiology and cardiometabolic diseases by interacting directly with intestinal cells or by producing molecules that enter the host circulation. Given the large number of microbial species present in the gut and the numerous factors that influence gut bacterial composition, it has been challenging to understand the underlying biological mechanisms that modulate risk of cardiometabolic disease.

SCOPE OF THE REVIEW

Here we discuss a systems-based approach that involves simultaneously examining individuals in populations for gut microbiome composition, molecular traits using "omics" technologies, such as circulating metabolites quantified by mass spectrometry, and clinical traits. We summarize findings from landmark studies using this approach and discuss future applications.

MAJOR CONCLUSIONS

Population-based integrative approaches have identified a large number of microbe-derived or microbe-modified metabolites that are associated with cardiometabolic traits. The knowledge gained from these studies provide new opportunities for understanding the mechanisms involved in gut microbiome-host interactions and may have potentially important implications for developing novel therapeutic approaches.

Gut Microbiota Modulation as a Novel Therapeutic Strategy in Cardiometabolic Diseases

The human gut harbors microbial ecology that is in a symbiotic relationship with its host and has a vital function in keeping host homeostasis. Inimical alterations in the composition of gut microbiota, known as gut dysbiosis, have been associated with cardiometabolic diseases. Studies have revealed the variation in gut microbiota composition in healthy individuals as compared to the composition of those with cardiometabolic diseases. Perturbation of host-microbial interaction attenuates physiological processes and may incite several cardiometabolic disease pathways. This imbalance contributes to cardiometabolic diseases via metabolism-independent and metabolite-dependent pathways. The aim of this review was to elucidate studies that have demonstrated the complex relationship between the intestinal microbiota as well as their metabolites and the development/progression of cardiometabolic diseases. Furthermore, we systematically itemized the potential therapeutic approaches for cardiometabolic diseases that target gut microbiota and/or their metabolites by following the pathophysiological pathways of disease development. These approaches include the use of diet, prebiotics, and probiotics. With the exposition of the link between gut microbiota and cardiometabolic diseases, the human gut microbiota therefore becomes a potential therapeutic target in the development of novel cardiometabolic agents.

Theacrine ameliorates experimental liver fibrosis in rats by lowering cholesterol storage via activation of the Sirtuin 3-farnesoid X receptor signaling pathway

Formulations against liver fibrosis (LF) mitigate the progression of hepatitis to cirrhosis. However, notable toxicity of the currently available anti-LF drugs limits their long-term use. In the study, we aimed to investigate the anti-LF effects of theacrine, a purine alkaloid without obvious toxicity, on high-fat diet-, alcohol-, and carbon tetrachloride-induced LF in rats. The results indicated that 10 and 20 mg/kg of theacrine ameliorated hepatic fibrosis, steatosis, and inflammation in LF rats. Mechanistically, theacrine reduced hepatic stellate cell (HSC)-related α-smooth muscle actin expression, and decreased cholesterol accumulation, followed by decreased expression of transforming growth factor-β1, interleukin (IL)-1β, and tumor necrosis factor (TNF)-α. In addition, theacrine upregulated the phosphorylation of AMP-activated protein kinase, accompanied by decreased expression of β-catenin and stearoyl-CoA desaturase 1, and increased the expression of sirtuin 3 (SIRT3). Further investigation revealed that the theacrine-mediated decrease in cholesterol was independent of cholesterol synthesis or low-density lipoprotein (LDL) uptake in hyperlipidemia mice. However, theacrine activated farnesoid X receptor (FXR), a β-catenin conjugated protein, accompanied with decreased expression of cholesterol 7α-hydroxylase and sterol 12α-hydroxylase. In conclusion, theacrine alleviated experimental LF in rats by lowering cholesterol storage and decreasing cholesterol-related HSC activation. A plausible mechanism of theacrine on cholesterol metabolism may involve activation of SIRT3-FXR signaling pathway followed by decreased intestinal cholesterol absorption.

Reduced Cytokine Tumour Necrosis Factor by Pharmacological Intervention in a Preclinical Study

Recent preclinical studies in our laboratory have shown that the bile acid profile is altered during diabetes development and such alteration has been linked to the diabetes-associated inflammatory profile. Hence, this study aimed to investigate if the first-line antidiabetic drug metformin will alter the bile acid profile and diabetes-associated inflammation in a murine model of pre-type 2 diabetes. C57 mice were randomly allocated into three equal groups of eight. Group One was given a low-fat diet (LFD), Group Two was given a high-fat diet (HFD), and Group Three was given an HFD and, upon prediabetes confirmation, daily oral metformin for one month. Blood glucose, glycated haemoglobin, drug concentrations in tissues and faeces, and the inflammatory and bile acid profiles were measured. Metformin showed wide tissue distribution and was also present in faeces. The bile acid profile showed significant alteration due to prediabetes, and although metformin did not completely normalize it, it did exert significant effects on both the bile acid and the inflammatory profiles, suggesting a direct and, to some extent, positive impact, particularly on the diabetes-associated inflammatory profile.

Monitoring Leukocyte Migration During Atherosclerosis In Vivo

Transendothelial leukocyte migration is an early event in the progression of vascular inflammation, the underlying molecular mechanism of atherosclerosis. Inflammatory mediators such as adhesion molecules and chemokines are essential in this process. Leukocyte migration into the vascular wall can be monitored by the detection of CD11b-positive immune cells in animal models of atherosclerosis. This chapter will describe an immunohistochemical technique used to evaluate leukocyte migration in vivo.

Atorvastatin protects against liver and vascular damage in a model of diet induced steatohepatitis by resetting FXR and GPBAR1 signaling

Farnesoid-x-receptor (FXR) agonists, currently trialed in patients with non-alcoholic steatosis (NAFLD), worsen the pro-atherogenic lipid profile and might require a comedication with statin. Here we report that mice feed a high fat/high cholesterol diet (HFD) are protected from developing a pro-atherogenic lipid profile because their ability to dispose cholesterol through bile acids. This protective mechanism is mediated by suppression of FXR signaling in the liver by muricholic acids (MCAs) generated in mice from chenodeoxycholic acid (CDCA). In contrast to CDCA, MCAs are FXR antagonists and promote a CYP7A1-dependent increase of bile acids synthesis. In mice feed a HFD, the treatment with obeticholic acid, a clinical stage FXR agonist, failed to improve the liver histopathology while reduced Cyp7a1 and Cyp8b1 genes expression and bile acids synthesis and excretion. In contrast, treating mice with atorvastatin mitigated liver and vascular injury caused by the HFD while increased the bile acids synthesis and excretion. Atorvastatin increased the percentage of 7α-dehydroxylase expressing bacteria in the intestine promoting the formation of deoxycholic acid and litocholic acid, two GPBAR1 agonists, along with the expression of GPBAR1-regulated genes in the white adipose tissue and colon. In conclusion, present results highlight the central role of bile acids in regulating lipid and cholesterol metabolism in response to atorvastatin and provide explanations for limited efficacy of FXR agonists in the treatment of NAFLD.

The Effects of PPAR Agonists on Atherosclerosis and Nonalcoholic Fatty Liver Disease in ApoE-/-FXR-/- Mice

BACKGROUND

Farnesoid X receptor (FXR), a bile acid-activated nuclear receptor, is a potent regulator of glucose and lipid metabolism as well as of bile acid metabolism. Previous studies have demonstrated that FXR deficiency is associated with metabolic derangements, including atherosclerosis and nonalcoholic fatty liver disease (NAFLD), but its mechanism remains unclear. In this study, we investigated the role of FXR in atherosclerosis and NAFLD and the effect of peroxisome proliferator-activated receptor (PPAR) agonists in mouse models with FXR deficiency.

METHODS

En face lipid accumulation analysis, liver histology, serum levels of glucose and lipids, and mRNA expression of genes related to lipid metabolism were compared between apolipoprotein E (ApoE)-/- and ApoE-/-FXR-/- mice. The effects of PPARα and PPARγ agonists were also compared in both groups of mice.

RESULTS

Compared with ApoE-/- mice, ApoE-/-FXR-/- mice showed more severe atherosclerosis, hepatic steatosis, and higher levels of serum cholesterol, low-density lipoprotein cholesterol, and triglycerides, accompanied by increased mRNA expression of FAS, ApoC2, TNFα, IL-6 (liver), ATGL, TGH, HSL, and MGL (adipocytes), and decreased mRNA expressions of CPT2 (liver) and Tfam (skeletal muscle). Treatment with a PPARα agonist, but not with a PPARγ agonist, partly reversed atherosclerosis and hepatic steatosis, and decreased plasma triglyceride levels in the ApoE-/-FXR-/- mice, in association with increased mRNA expression of CD36 and FATP and decreased expression of ApoC2 and ApoC3 (liver).

CONCLUSION

Loss of FXR is associated with aggravation of atherosclerosis and hepatic steatosis in ApoE-deficient mice, which could be reversed by a PPARα agonist through induction of fatty acid uptake, β-oxidation, and triglyceride hydrolysis.

Linking liver metabolic and vascular disease via bile acid signaling

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disorder affecting over one quarter of the global population. Liver fat accumulation in NAFLD is promoted by increased de novo lipogenesis leading to the development of a proatherosclerotic lipid profile and atherosclerotic cardiovascular disease (CVD). The CVD component of NAFLD is the main determinant of patient outcome. The farnesoid X receptor (FXR) and the G protein bile acid-activated receptor 1 (GPBAR1) are bile acid-activated receptors that modulate inflammation and lipid and glucose metabolism in the liver and CV system, and are thus potential therapeutic targets. We review bile acid signaling in liver, metabolic tissues, and the CV system, and we propose the development of dual FXR/GPBAR1 ligands, intestine-restricted FXR ligands, or statin combinations to limit side effects and effectively manage the liver and CV components of NAFLD.

Circulating bile acids concentration is predictive of coronary artery disease in human

Synthetized by the liver and metabolized by the gut microbiota, BA are involved in metabolic liver diseases that are associated with cardiovascular disorders. Animal models of atheroma documented a powerful anti-atherosclerotic effect of bile acids (BA). This prospective study examined whether variations in circulating BA are predictive of coronary artery disease (CAD) in human. Consecutive patients undergoing coronary angiography were enrolled. Circulating and fecal BA were measured by high pressure liquid chromatography and tandem mass spectrometry. Of 406 screened patients, 80 were prospectively included and divided in two groups with (n = 45) and without (n = 35) CAD. The mean serum concentration of total BA was twice lower in patients with, versus without CAD (P = 0.005). Adjusted for gender and age, this decrease was an independent predictor of CAD. In a subgroup of 17 patients, statin therapy doubled the serum BA concentration. Decreased serum concentrations of BA were predictors of CAD in humans. A subgroup analysis showed a possible correction by statins. With respect to the anti-atherosclerotic effect of BA in animal models, and their role in human lipid metabolism, this study describe a new metabolic disturbance associated to CAD in human.

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.

Upregulation of FOXP3 is associated with severity of hypoxia and poor outcomes in COVID-19 patients

The levels of messenger RNA (mRNA) transcription of FOXP3, IFN-γ, TNF, IL-6 and COX-2 from both COVID-19 infected and control subjects were evaluated using SYBR^TM green real-time polymerase chain reaction (RT-PCR). Severe/critical cases showed significantly lower lymphocyte counts and higher neutrophil counts than the mild or moderate cases. There were significantly lower levels of mRNA expressions of IFN-γ, TNFα and FOXP3 in COVID-19 patients than in the control group. On the other hand, IL-6 and COX-2 expressions were significantly higher in patients suffering from severe disease. FOXP3 expressions were correlated with the severities of hypoxia and were excellent in predicting the disease severity. This was followed by the IL-6, COX-2 and TNFα expressions. FOXP3 expression was the only biomarker to show a significant correlation with patient mortality. It was concluded that SARS-CoV-2 infection is associated with the downregulation of FOXP3 and upregulations of IL-6 and COX-2.

Cigarette smoke extract combined with LPS down-regulates the expression of MRP2 in chronic pulmonary inflammation may be related to FXR

The transporter multidrug resistance protein 2 (MRP2) plays an important role in chronic pulmonary inflammation by transporting cigarette smoke and other related inflammatory mediators. However, it is not completely clear whether pulmonary inflammation caused by cigarette smoke extract (CSE) and lipopolysaccharide (LPS) is related to MRP2 and its signal factors. In this study, CSE combined with LPS was used to establish an inflammation model in vivo and in vitro. We found that compared with the control group, after CSE combined with LPS treatment, the expression of MRP2 in rat lung tissue in vivo and human alveolar cell line in vitro was down-regulated, while the expression of inflammatory factors was up-regulated. Through silencing and overexpression of FXR, it was found that silent FXR could down-regulate MRP2 and up-regulate the expression of inflammatory factors. On the contrary, overexpression of FXR could up-regulate MRP2 and down-regulate the expression of inflammatory factors. Our results show that CSE combined with LPS can down-regulate the expression of MRP2 under inflammatory conditions, and the down-regulation of MRP2 expression may be achieved partly through the FXR signal pathway.

Association between Pre-Diagnostic Serum Bile Acids and Hepatocellular Carcinoma: The Singapore Chinese Health Study

Hepatocellular carcinoma (HCC) is a commonly diagnosed malignancy with poor prognosis. Rising incidence of HCC may be due to rising prevalence of metabolic dysfunction-associated fatty liver disease, where altered bile acid metabolism may be implicated in HCC development. Thirty-five bile acids were quantified using ultra-performance liquid chromatography triple-quadrupole mass spectrometry assays in pre-diagnostic serum of 100 HCC cases and 100 matched controls from the Singapore Chinese Health Study. Conditional logistic regression was used to assess associations for bile acid levels with risk of HCC. Conjugated primary bile acids were significantly elevated whereas the ratios of secondary bile acids over primary bile acids were significantly lower in HCC cases than controls. The respective odds ratios and 95% confidence intervals of HCC were 6.09 (1.75-21.21) for highest vs. lowest tertile of cholic acid species and 30.11 (5.88-154.31) for chenodeoxycholic acid species. Doubling ratio of taurine-over glycine-conjugated chenodeoxycholic acid was associated significantly with 40% increased risk of HCC whereas doubling ratio of secondary over primary bile acid species was associated with 30-40% reduced risk of HCC. In conclusion, elevated primary bile acids and taurine over glycine-conjugated ratios were strongly associated with HCC risk whereas the ratios of secondary bile acids over primary bile acids were inversely associated with HCC risk.

The identification of farnesoid X receptor modulators as treatment options for nonalcoholic fatty liver disease

INTRODUCTION

The farnesoid-x-receptor (FXR) is a ubiquitously expressed nuclear receptor selectively activated by primary bile acids.

AREA COVERED

FXR is a validated pharmacological target. Herein, the authors review preclinical and clinical data supporting the development of FXR agonists in the treatment of nonalcoholic fatty liver disease.

EXPERT OPINION

Development of systemic FXR agonists to treat the metabolic liver disease has been proven challenging because the side effects associated with these agents including increased levels of cholesterol and LDL-c and reduced HDL-c raising concerns over their long-term cardiovascular safety. Additionally, pruritus has emerged as a common, although poorly explained, dose-related side effect with all FXR ligands, but is especially common with OCA. FXR agonists that are currently undergoing phase 2/3 trials are cilofexor, tropifexor, nidufexor and MET409. Some of these agents are currently being developed as combination therapies with other agents including cenicriviroc, a CCR2/CCR5 inhibitor, or firsocostat an acetyl CoA carboxylase inhibitor. Additional investigations are needed to evaluate the beneficial effects of combination of these agents with statins. It is expected that in the coming years, FXR agonists will be developed as a combination therapy to minimize side effects and increase likelihood of success by targeting different metabolic pathways.

Gut microbiota in coronary artery disease: a friend or foe?

There is a growing interest in the role of gut microbiota in the pathophysiology of several diseases, including coronary artery diseases (CAD). Gut microorganisms may produce beneficial effects in myocardial ischemia either directly in the form of exogenous administration or indirectly by acting on fiber-rich food to produce important cardioprotective components. The harmful effects of gut microbiota in CAD are due to alteration in their composition with a significant decrease in Bacteroidetes and an increase in Firmicutes, Escherichia, Shigella, and Enterococcus. The altered microbiota may produce potentially toxic metabolites, including trimethylamine-N-oxide (TMAO). Indeed, the fasting plasma levels of TMAO are directly correlated to increased risk of major cardiovascular events in CAD patients, and it is proposed as a potential biomarker to predict the onset of major cardiovascular events. It is concluded that the change in the composition of gut microbiota in CAD patients may predispose to more harmful effects. However, exogenous delivery of probiotics may overcome the detrimental effects of myocardial ischemia.

Bile acids profile, histopathological indices and genetic variants for non-alcoholic fatty liver disease progression

OBJECTIVE

Metabolomic studies suggest plasma levels of bile acids (BAs) are elevated amongst subjects with non-alcoholic fatty liver disease (NAFLD) compared to healthy controls. However, it remains unclear whether or not specific BAs are associated with the clinically relevant transition from nonalcoholic fatty liver (i.e. simple steatosis) to non-alcoholic steatohepatitis (NASH), or enhanced progression of hepatic fibrosis, or genetic determinants of NAFLD/NASH.

METHODS

Among sequential subjects (n=102) undergoing diagnostic liver biopsy, we examined the associations of a broad panel of BAs with distinct histopathological features of NAFLD, the presence of NASH, and their associations with genetic variants linked to NAFLD and NASH.

RESULTS

Plasma BA alterations were observed through the entire spectrum of NAFLD, with several glycine conjugated forms of the BAs demonstrating significant associations with higher grades of inflammation and fibrosis. Plasma 7-Keto-DCA levels showed the strongest associations with advanced stages of hepatic fibrosis [odds ratio(95% confidence interval)], 4.2(1.2-16.4), NASH 24.5(4.1-473), and ballooning 18.7(4.8-91.9). Plasma 7-Keto-LCA levels were associated with NASH 9.4(1.5-185) and ballooning 5.9(1.4-28.8). Genetic variants at several NAFLD/NASH loci were nominally associated with increased levels of 7-Keto- and glycine-conjugated forms of BAs, and the NAFLD risk allele at the TRIB1 locus showed strong tendency toward increased plasma levels of GCA (p=0.02) and GUDCA (p=0.009).

CONCLUSIONS

Circulating bile acid levels are associated with histopathological and genetic determinants of the transition from simple hepatic steatosis into NASH. Further studies exploring the potential involvement of bile acid metabolism in the development and/or progression of distinct histopathological features of NASH are warranted.

Bile acids and their receptors in metabolic disorders

Bile acids are a large family of atypical steroids which exert their functions by binding to a family of ubiquitous cell membrane and nuclear receptors. There are two main bile acid activated receptors, FXR and GPBAR1, that are exclusively activated by bile acids, while other receptors CAR, LXRs, PXR, RORγT, S1PR2and VDR are activated by bile acids in addition to other more selective endogenous ligands. In the intestine, activation of FXR and GPBAR1 promotes the release of FGF15/19 and GLP1 which integrate their signaling with direct effects exerted by theother receptors in target tissues. This network is tuned in a time ordered manner by circadian rhythm and is critical for the regulation of metabolic process including autophagy, fast-to-feed transition, lipid and glucose metabolism, energy balance and immune responses. In the last decade FXR ligands have entered clinical trials but development of systemic FXR agonists has been proven challenging because their side effects including increased levels of cholesterol and Low Density Lipoproteins cholesterol (LDL-c) and reduced High-Density Lipoprotein cholesterol (HDL-c). In addition, pruritus has emerged as a common, dose related, side effect of FXR ligands. Intestinal-restricted FXR and GPBAR1 agonists and dual FXR/GPBAR1 agonists have been developed. Here we review the last decade in bile acids physiology and pharmacology.

The Liver under the Spotlight: Bile Acids and Oxysterols as Pivotal Actors Controlling Metabolism

Among the myriad of molecules produced by the liver, both bile acids and their precursors, the oxysterols are becoming pivotal bioactive lipids which have been underestimated for a long time. Their actions are ranging from regulation of energy homeostasis (i.e., glucose and lipid metabolism) to inflammation and immunity, thereby opening the avenue to new treatments to tackle metabolic disorders associated with obesity (e.g., type 2 diabetes and hepatic steatosis) and inflammatory diseases. Here, we review the biosynthesis of these endocrine factors including their interconnection with the gut microbiota and their impact on host homeostasis as well as their attractive potential for the development of therapeutic strategies for metabolic disorders.

Transcriptional Regulation of Metabolic Pathways via Lipid-Sensing Nuclear Receptors PPARs, FXR, and LXR in NASH

Nonalcoholic fatty liver disease comprises a wide spectrum of liver injuries from simple steatosis to steatohepatitis and cirrhosis. Nonalcoholic steatohepatitis (NASH) is defined when liver steatosis is associated with inflammation, hepatocyte damage, and fibrosis. A genetic predisposition and environmental insults (ie, dietary habits, obesity) are putatively responsible for NASH progression. Here, we present the impact of the lipid-sensing nuclear receptors in the pathogenesis and treatment of NASH. In detail, we discuss the pros and cons of the putative transcriptional action of the fatty acid sensors (peroxisome proliferator-activated receptors), the bile acid sensor (farnesoid X receptor), and the oxysterol sensor (liver X receptors) in the pathogenesis and bona fide treatment of NASH.

Nuclear Receptors in Asthma: Empowering Classical Molecules Against a Contemporary Ailment

The escalation in living standards and adoption of 'Western lifestyle' has an allied effect on the increased allergy and asthma burden in both developed and developing countries. Current scientific reports bespeak an association between allergic diseases and metabolic dysfunction; hinting toward the critical requirement of organized lifestyle and dietary habits. The ubiquitous nuclear receptors (NRs) translate metabolic stimuli into gene regulatory signals, integrating diet inflences to overall developmental and physiological processes. As a consequence of such promising attributes, nuclear receptors have historically been at the cutting edge of pharmacy world. This review discusses the recent findings that feature the cardinal importance of nuclear receptors and how they can be instrumental in modulating current asthma pharmacology. Further, it highlights a possible future employment of therapy involving dietary supplements and synthetic ligands that would engage NRs and aid in eliminating both asthma and linked comorbidities. Therefore, uncovering new and evolving roles through analysis of genomic changes would represent a feasible approach in both prevention and alleviation of asthma.

Role of Gut Microbiota and Their Metabolites on Atherosclerosis, Hypertension and Human Blood Platelet Function: A Review

Emerging data have demonstrated a strong association between the gut microbiota and the development of cardiovascular disease (CVD) risk factors such as atherosclerosis, inflammation, obesity, insulin resistance, platelet hyperactivity, and plasma lipid abnormalities. Several studies in humans and animal models have demonstrated an association between gut microbial metabolites such as trimethylamine-N-oxide (TMAO), short-chain fatty acids, and bile acid metabolites (amino acid breakdown products) with CVD. Human blood platelets are a critical contributor to the hemostatic process. Besides, these blood cells play a crucial role in developing atherosclerosis and, finally, contribute to cardiac events. Since the TMAO, and other metabolites of the gut microbiota, are asociated with platelet hyperactivity, lipid disorders, and oxidative stress, the diet-gut microbiota interactions have become an important research area in the cardiovascular field. The gut microbiota and their metabolites may be targeted for the therapeutic benefit of CVD from a clinical perspective. This review's main aim is to highlight the complex interactions between microbiota, their metabolites, and several CVD risk factors.

Enterohepatic circulation of bile acids and their emerging roles on glucolipid metabolism

Bile acids (BAs) are amphiphilic molecules with a nonpolar steroid carbon skeleton and a polar carboxylate side chain. Recently, BAs have aroused the attention of scholars due to their potential roles on metabolic diseases. As important endogenous ligands, BAs are wildly active in the enterohepatic circulation, during which microbiota play a significant role in promoting the hydrolysis and dehydroxylation of BAs. Besides, many pathways initiated by BAs including glucolipid metabolism and inflammation signaling pathways have been reported to regulate the host metabolism and maintain immune homeostasis. Herein, the characteristics on the enterohepatic circulation and metabolism of BAs are systematically summarized. Moreover, the regulation mechanism of the glucolipid metabolism by BAs is intensively discussed. Worthily, FXR and TGR5, which are involved in glucolipid metabolism, are the prime candidates for targeted therapies of chronic metabolic diseases such as diabetes and hypercholesterolemia.

Mutual Interplay of Host Immune System and Gut Microbiota in the Immunopathology of Atherosclerosis

Inflammation is the key for the initiation and progression of atherosclerosis. Accumulating evidence has revealed that an altered gut microbiome (dysbiosis) triggers both local and systemic inflammation to cause chronic inflammatory diseases, including atherosclerosis. There have been some microbiome-relevant pro-inflammatory mechanisms proposed to link the relationships between dysbiosis and atherosclerosis such as gut permeability disruption, trigger of innate immunity from lipopolysaccharide (LPS), and generation of proatherogenic metabolites, such as trimethylamine N-oxide (TMAO). Meanwhile, immune responses, such as inflammasome activation and cytokine production, could reshape both composition and function of the microbiota. In fact, the immune system delicately modulates the interplay between microbiota and atherogenesis. Recent clinical trials have suggested the potential of immunomodulation as a treatment strategy of atherosclerosis. Here in this review, we present current knowledge regarding to the roles of microbiota in contributing atherosclerotic pathogenesis and highlight translational perspectives by discussing the mutual interplay between microbiota and immune system on atherogenesis.

Understanding connections and roles of gut microbiome in cardiovascular diseases

The gut microbiome encompasses trillions of residing microbes, mainly bacteria, which play a crucial role in maintaining the physiological and metabolic health of the host. The gut microbiome has been associated with several diseases, including cardiovascular disease (CVD). A growing body of evidence suggests that an altered gut environment and gut-microbiome-derived metabolites are associated with CVD events. The gut microbiome communicates with host physiology through different mechanisms, including trimethylamine N-oxide generation, primary and secondary bile acid metabolism pathways, and short-chain fatty acids production. The main focus of this review is to understand the association of the gut microbiome with CVD and its implications on the interactions between the gut microbiome and the host. Manipulation of the gut microbiome through specific dietary intervention is a simple approach to identifying novel targets for therapy or better dietary recommendations, and new preventive measures for screening biomarkers to reduce CVD risk in humans.

An insight into primary biliary cholangitis and its recent advances in treatment: semi-synthetic analogs to combat ursodeoxycholic-acid resistance

INTRODUCTION

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease which on progression causes cirrhosis; various studies also suggested that several diseases can co-exist in patients. In existing depiction of disease PBC, apart from entire use of ursodeoxycholic acid (UDCA), several patients need to step forward to liver-transplantation or death due to resistance or non-responder with UDCA monotherapy.

AREAS COVERED

To overcome this non-respondent treatment, novel bile acid semi-synthetic analogs have been identified which shows their potency against for farnesoid X receptor and transmembrane G protein-coupled receptor-5 which are identified as target for many developing analogs which have desirable pharmacokinetic profiles.

EXPERT OPINION

A range of studies suggests that adding semisynthetic analogs in therapeutic regime improves liver biochemistries in patients with suboptimal response to UDCA. Thus, the aspire of this review is to abridge and compare therapeutic value and current markets affirm of various bile acids semi-synthetic analogs which certainly are having promising effects in PBC monotherapy or in pooled treatment with UDCA for PBC.

Gut Microbiota: A Key Factor in the Host Health Effects Induced by Pesticide Exposure?

In the past few decades, a large number of pesticides have been widely used for plant protection. Pesticides may enter non-target organisms through multiple ways and bring potential health risks. There is a dense and diverse microbial community in the intestines of mammals, which is called the gut microbiota. The gut microbiota and its metabolites play vital roles in maintaining the health of the host. Interestingly, many studies have shown that exposure to multiple pesticides could affect the gut microbiota of the host. However, the roles of gut microbiota and its related metabolites in the host health effects induced by pesticide exposure of non-target organisms need further study. We reviewed the relationships between pesticide exposure and host health effects as well as between the gut microbiota and host health effects. Importantly, we reviewed the latest research on the gut microbiota and its metabolites in the host health effects induced by pesticide exposure.

Gut Microbiota in Hypertension and Atherosclerosis: A Review

Gut microbiota and its metabolites such as short chain fatty acids (SCFA), lipopolysaccharides (LPS), and trimethylamine-N-oxide (TMAO) impact cardiovascular health. In this review, we discuss how gut microbiota and gut metabolites can affect hypertension and atherosclerosis. Hypertensive patients were shown to have lower alpha diversity, lower abundance of SCFA-producing microbiota, and higher abundance of gram-negative bacteria, which are a source of LPS. Animal studies point towards a direct role for SCFAs in blood pressure regulation and show that LPS has pro-inflammatory effects. Translocation of LPS into the systemic circulation is a consequence of increased gut permeability. Atherosclerosis, a multifactorial disease, is influenced by the gut microbiota through multiple pathways. Many studies have focused on the pro-atherogenic role of TMAO, however, it is not clear if this is a causal factor. In addition, gut microbiota play a key role in bile acid metabolism and some interventions targeting bile acid receptors tend to decrease atherosclerosis. Concluding, gut microbiota affect hypertension and atherosclerosis through many pathways, providing a wide range of potential therapeutic targets. Challenges ahead include translation of findings and mechanisms to humans and development of therapeutic interventions that target cardiovascular risk by modulation of gut microbes and metabolites.

Farnesoid X Receptor Agonists as Therapeutic Target for Cardiometabolic Diseases

Cardiometabolic diseases are characterized as a combination of multiple risk factors for cardiovascular disease (CVD) and metabolic diseases including diabetes mellitus and dyslipidemia. Cardiometabolic diseases are closely associated with cell glucose and lipid metabolism, inflammatory response and mitochondrial function. Farnesoid X Receptor (FXR), a metabolic nuclear receptor, are found to be activated by primary BAs such as chenodeoxycholic acid (CDCA), cholic acid (CA) and synthetic agonists such as obeticholic acid (OCA). FXR plays crucial roles in regulating cholesterol homeostasis, lipid metabolism, glucose metabolism, and intestinal microorganism. Recently, emerging evidence suggests that FXR agonists are functional for metabolic syndrome and cardiovascular diseases and are considered as a potential therapeutic agent. This review will discuss the pathological mechanism of cardiometabolic disease and reviews the potential mechanisms of FXR agonists in the treatment of cardiometabolic disease.

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.

Gut Microbiota and Heart, Vascular Injury

The gut microbiota plays an important role in maintaining human health. Accumulating evidence has indicated an intimate relationship between gut microbiota and cardiovascular diseases (CVD) which has become the leading cause of death worldwide. The alteration of gut microbial composition (gut dysbiosis) has been proven to contribute to atherosclerosis, the basic pathological process of CVD. In addition, the metabolites of gut microbiota have been found to be closely related to the development of CVD. For example, short-chain fatty acids are widely acclaimed beneficial effect against CVD, whereas trimethylamine-N-oxide is considered as a contributing factor in the development of CVD. In this chapter, we mainly discuss the gut microbial metabolite-involved mechanisms of CVD focusing on atherosclerosis, hypertension, diabetes, obesity, and heart failure. Targeting gut microbiota and related metabolites are novel and promising strategies for the treatment of CVD.

Gut microbiota: a promising target against cardiometabolic diseases

Introduction: Cardiometabolic diseases (CMD) are a group of interrelated disorders such as metabolic syndrome, type 2 diabetes mellitus and cardiovascular diseases (CVD). As the prevalence of these diseases increases globally, efficient new strategies are necessary to target CMD and modifiable risk factors. In the past decade, evidence has accumulated regarding the influence of gut microbiota (GM) on CMD, providing new targets for therapeutic interventions.Areas covered: This narrative review discusses the pathophysiologic link between CMD, GM, and potential microbiota-based targets against atherosclerosis and modifiable risk factors for atherosclerosis. Low-grade inflammation can be induced through GM and its derived metabolites. CMD are influenced by GM and microbiota-derived metabolites such as short-chain fatty acids (SCFA), secondary bile acids, trimethylamine N-oxide (TMAO), and the composition of GM can modulate host metabolism. All of the above can lead to promising therapeutic targets.Expert opinion: Most data are derived from animal models or human association studies; therefore, more translational and interventional research in humans is necessary to validate these promising findings. Reproduced findings such as aberrant microbiota patterns or circulating biomarkers could be targeted depending on individual metabolic profiles, moving toward personalized medicine in CMD.

Pioglitazone prevents cholesterol gallstone formation through the regulation of cholesterol homeostasis in guinea pigs with a lithogenic diet

Background

The cholesterol gallstones diseases (CGD) is highly correlated with metabolic syndrome and type 2 diabetes. The present study aimed to investigate preventive effects of pioglitazone (PIO), an antidiabetic drug, on the CGD in guinea pigs fed with a lithogenic diet (LD).

Methods

The guinea pigs were fed with the LD for 8 weeks. All guinea pigs were grouped as follows: low fat diet; LD; LD plus PIO (4 mg/kg); LD plus PIO (8 mg/kg); LD plus ezetimibe (EZE) (2 mg/kg). Gallbladder stones were observed using microscopy. The profile of biliary composition, and blood glucose, insulin and lipid were analyzed. The liver or ileum was harvested for determinations of hydroxyl-methyl-glutaryl-CoA reductase (HMGCR), sterol regulatory element-binding proteins 2 (SREBP2), 7α-hydroxylase (CYP7A1), adenosine triphosphate-binding cassette (ABC) sterol transporters G5 and G8 (ABCG5, ABCG8), bile salt export pump (BSEP), Niemann-Pick C1-Like 1 (NPC1L1) and acetyl-coenzyme A cholesterol acyltransferase (ACAT2) by Western blot. The gallbladders were used for histological examination.

Results

The LD successfully induced gallstone. Both pioglitazone and ezetimibe prevented gallstone formation, as well as hepatic and cholecystic damages. Pioglitazone significantly decreased HMGCR and SREBP2, but increased CYP7A1, ABCG5, ABCG8, and BSEP in the liver. Pioglitazone also remarkably decreased NPC1L1 and ACAT2, while increased ABCG5/8 in the intestine. The beneficial alterations of cholesterol and bile acids in the bile, as well as profile of glucose, insulin and lipid in the blood were found in the guinea pigs treated with pioglitazone.

Conclusion

Pioglitazone has a noticeable benefit towards the CGD, which is involved in changes of synthesis, transformation, absorption, and transportation of cholesterol.

Quantification of bile acids: a mass spectrometry platform for studying gut microbe connection to metabolic diseases

Bile acids (BAs) serve multiple biological functions, ranging from the absorption of lipids and fat-soluble vitamins to serving as signaling molecules through the direct activation of dedicated cellular receptors. Synthesized by both host and microbial pathways, BAs are increasingly understood as participating in the regulation of numerous pathways relevant to metabolic diseases, including lipid and glucose metabolism, energy expenditure, and inflammation. Quantitative analyses of BAs in biological matrices can be problematic due to their unusual and diverse physicochemical properties, making optimization of a method that shows good accuracy, precision, efficiency of extraction, and minimized matrix effects across structurally distinct human and murine BAs challenging. Herein we develop and clinically validate a stable-isotope-dilution LC/MS/MS method for the quantitative analysis of numerous primary and secondary BAs in both human and mouse biological matrices. We also utilize this tool to investigate gut microbiota participation in the generation of structurally specific BAs in both humans and mice. We examine circulating levels of specific BAs and in a clinical case-control study of age- and gender-matched type 2 diabetes mellitus (T2DM) versus nondiabetics. BAs whose circulating levels are associated with T2DM include numerous 12α-hydroxyl BAs (taurocholic acid, taurodeoxycholic acid, glycodeoxycholic acid, deoxycholic acid, and 3-ketodeoxycholic acid), while taurohyodeoxycholic acid was negatively associated with diabetes. The LC/MS/MS-based platform described should serve as a robust, high-throughput investigative tool for studying the potential involvement of structurally specific BAs and the gut microbiome on both physiological and disease processes.