Bile acids increase intracellular Ca(2+) concentration and nitric oxide production in vascular endothelial cells

Bile Acid Application in Cell-Targeting for Molecular Receptors in Relation to Hearing: A Comprehensive Review

Bile acids play important roles in the human body, and changes in their pool can be used as markers for various liver pathologies. In addition to their functional effects in modulating inflammatory responses and cellular survivability, the unconjugated or conjugated, secondary, or primary nature of bile acids accounts for their various ligand effects. The common hydrophilic bile acids have been used successfully as local treatment to resolve drug-induced cell damage or to ameliorate hearing loss. From various literature references, bile acids show concentration and tissue-dependent effects. Some hydrophobic bile acids act as ligands modulating vitamin D receptors, muscarinic receptors, and calcium-activated potassium channels, important proteins in the inner ear system. Currently, there are limited resources investigating the therapeutic effects of bile acid on hearing loss and little to no information on detecting bile acids in the remote ear system, let alone baseline bile acid levels and their prevalence in healthy and disease conditions. This review presents both hydrophilic and hydrophobic human bile acids and their tissue-specific effects in modulating cellular integrity, thus considering the possible effects and extended therapeutic applicability of bile acids to the inner ear tissue.

Deoxycholic Acid, a Secondary Bile Acid, Increases Cardiac Output and Blood Pressure in Rats

BACKGROUND

Deoxycholic acid (DCA) is a secondary bile acid produced by gut bacteria. Elevated serum concentrations of DCA are observed in cardiovascular disease (CVD). We hypothesized that DCA might influence hemodynamic parameters in rats.

METHODS

The concentration of DCA in systemic blood was measured with liquid chromatography coupled with mass spectrometry. Arterial blood pressure (BP), heart rate (HR) and echocardiographic parameters were evaluated in anesthetized, male, 3-4-month-old Sprague-Dawley rats administered intravenously (IV) or intracerebroventricularly (ICV) with investigated compounds. Mesenteric artery (MA) reactivity was tested ex vivo.

RESULTS

The baseline plasma concentration of DCA was 0.24 ± 0.03 mg/L. The oral antibiotic treatment produced a large decrease in the concentration. Administered IV, the compound increased BP and HR in a dose-dependent manner. DCA also increased heart contractility and cardiac output. None of the tested compounds-prazosin (an alpha-blocker), propranolol (beta-adrenolytic), atropine (muscarinic receptor antagonist), glibenclamide (K-ATP inhibitor) or DY 268 (FXR antagonist), glycyrrhetinic acid (11HSD2 inhibitor)-significantly diminished the DCA-induced pressor effect. ICV infusion did not exert significant HR or BP changes. DCA relaxed MAs. Systemic vascular resistance did not change significantly.

CONCLUSIONS

DCA elevates BP primarily by augmenting cardiac output. As a metabolite derived from gut bacteria, DCA potentially serves as a mediator in the interaction between the gut microbiota and the host's circulatory system.

The Dynamic Role of Endoplasmic Reticulum Stress in Chronic Liver Disease

Chronic liver disease (CLD) is a major worldwide public health threat, with an estimated prevalence of 1.5 billion individuals with CLD in 2020. Chronic activation of endoplasmic reticulum (ER) stress-related pathways is recognized as substantially contributing to the pathologic progression of CLD. The ER is an intracellular organelle that folds proteins into their correct three-dimensional shapes. ER-associated enzymes and chaperone proteins highly regulate this process. Perturbations in protein folding lead to misfolded or unfolded protein accumulation in the ER lumen, resulting in ER stress and concomitant activation of the unfolded protein response (UPR). The adaptive UPR is a set of signal transduction pathways evolved in mammalian cells that attempts to reestablish ER protein homeostasis by reducing protein load and increasing ER-associated degradation. However, maladaptive UPR responses in CLD occur due to prolonged UPR activation, leading to concomitant inflammation and cell death. This review assesses the current understanding of the cellular and molecular mechanisms that regulate ER stress and the UPR in the progression of various liver diseases and the potential pharmacologic and biological interventions that target the UPR.

AIBP Regulates Metabolism of Ketone and Lipids but Not Mitochondrial Respiration

Accumulating evidence indicates that the APOA1 binding protein (AIBP)-a secreted protein-plays a profound role in lipid metabolism. Interestingly, AIBP also functions as an NAD(P)H-hydrate epimerase to catalyze the interconversion of NAD(P)H hydrate [NAD(P)HX] epimers and is renamed as NAXE. Thus, we call it NAXE hereafter. We investigated its role in NAD(P)H-involved metabolism in murine cardiomyocytes, focusing on the metabolism of hexose, lipids, and amino acids as well as mitochondrial redox function. Unbiased metabolite profiling of cardiac tissue shows that NAXE knockout markedly upregulates the ketone body 3-hydroxybutyric acid (3-HB) and increases or trends increasing lipid-associated metabolites cholesterol, α-linolenic acid and deoxycholic acid. Paralleling greater ketone levels, ChemRICH analysis of the NAXE-regulated metabolites shows reduced abundance of hexose despite similar glucose levels in control and NAXE-deficient blood. NAXE knockout reduces cardiac lactic acid but has no effect on the content of other NAD(P)H-regulated metabolites, including those associated with glucose metabolism, the pentose phosphate pathway, or Krebs cycle flux. Although NAXE is present in mitochondria, it has no apparent effect on mitochondrial oxidative phosphorylation. Instead, we detected more metabolites that can potentially improve cardiac function (3-HB, adenosine, and α-linolenic acid) in the Naxe^-/- heart; these mice also perform better in aerobic exercise. Our data reveal a new role of NAXE in cardiac ketone and lipid metabolism.

Renal Farnesoid X Receptor improves high fructose-induced salt-sensitive hypertension in mice by inhibiting DNM3 to promote nitro oxide production

OBJECTIVE

Farnesoid X Receptor (FXR) is highly expressed in renal tubules, activation of which attenuates renal injury by suppressing inflammation and fibrosis. However, whether renal FXR contributes to the regulation of blood pressure (BP) is poorly understood. This study aimed to investigate the anti-hypertensive effect of renal FXR on high-fructose-induced salt-sensitive hypertension and underlying mechanism.

METHODS

Hypertension was induced in male C57BL/6 mice by 20% fructose in drinking water with 4% sodium chloride in diet (HFS) for 8 weeks. The effects of FXR on NO production were estimated in vitro and in vivo.

RESULTS

Compared with control, HFS intake elevated BP, enhanced renal injury and reduced renal NO levels as well as FXR expression in the kidney of mice. In the mouse renal collecting duct cells mIMCD-K2, FXR agonists promoted NO production by enhancing the expression of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS), whereas this effect was diminished by fxr knockdown. We further found that Dynamin 3 (DNM3), a binding protein with nNOS in the renal medulla, was inhibited by FXR and its deficiency elevated NO production in mIMCD-K2 cells. In HFS-fed mice, renal fxr overexpression significantly attenuated hypertension and renal fibrosis, regulated the expression of DNM3/nNOS/iNOS, and increased renal NO levels.

CONCLUSION

Our results demonstrated that renal FXR prevents HFS-induced hypertension by inhibiting DNM3 to promote NO production. These findings provide insights into the role and potential mechanism of renal FXR for the treatment of hypertension.

Moderation of gut microbiota and bile acid metabolism by chlorogenic acid improves high-fructose-induced salt-sensitive hypertension in mice

Chlorogenic acid (CGA) is a natural compound with many important pharmacological effects including anti-hypertension. This study aimed to investigate the anti-hypertensive effect of CGA on high-fructose-induced salt-sensitive hypertension and the underlying mechanism. Hypertension was induced in male C57BL/6 mice by 20% fructose in drinking water plus 4% sodium chloride in the diet (HFS) for 8 weeks. CGA (50, 100 or 200 mg kg^-1 d^-1) was orally administered to HFS-treated mice. The blood pressure of mice was recorded via the tail cuff method. The structure of gut microbiota and profiles of bile acids (BAs) in the serum were determined. Here, we found that HFS-elevated systolic blood pressure was greatly attenuated by CGA. The microbiota analysis showed that CGA restructured the HFS-treated gut microbiota, and markedly enriched Klebsiella. Oral administration of a Klebsiella isolate, Klebsiella oxytoca, also exhibited an anti-hypertensive effect in HFS-fed mice. Furthermore, we found that CGA and CGA-enriched K. oxytoca enhanced the expression of colonic Farnesoid X Receptor (FXR), modulated BA metabolism and enriched some BAs including deoxycholic acid (DCA) in the serum of HFS-fed mice. Treatment with DCA improved phenylephrine-induced vasoconstriction in arterioles of mice and attenuated hypertension in HFS-fed mice, suggesting that DCA serves as a link between gut microbiota and blood pressure. Our results clearly demonstrate that CGA attenuates HFS-induced hypertension in mice by modulating gut microbiota and BA metabolism. These findings provide insights into the potential mechanism of CGA for the treatment of hypertension.

Bile acids-induced lung injury: update of reverse translational biology

The presence of bile acids in lung tissue is associated with some clinical features observed in various medical specialties, but it took time to understand that these are due to a "bile acid-induced lung injury" since specific translational studies and cross-disciplinary awareness were lacking. We used a reverse translational approach to update and summarize the current knowledge about the mechanisms of bile acid-induced lung injury. This has been done in a cross-disciplinary fashion since these conditions may occur in patients of various age and in different medical fields. We here define these clinical conditions, then we review the physiopathology of these conditions and the animal models used to mimic them and, finally, their pathobiology. Mechanisms of bile acid-induced lung injury have been partially clarified overtime and are represented by: 1) the interaction with secretory phospholipase A2 pathway, 2) the effect on surfactant function and structure, 3) the biological effects on inflammation and local immunity, 4) the direct cellular toxicity. These mechanisms are schematically illustrated and histological comparisons between ARDS induced by bile acids and other triggers are also provided. Based on these mechanisms we propose possible direct therapeutic applications and, finally, we discuss further research steps to improve the understanding of processes that generate pathological clinical conditions.

The Role of Bile Acids in the Human Body and in the Development of Diseases

Bile acids are specific and quantitatively important organic components of bile, which are synthesized by hepatocytes from cholesterol and are involved in the osmotic process that ensures the outflow of bile. Bile acids include many varieties of amphipathic acid steroids. These are molecules that play a major role in the digestion of fats and the intestinal absorption of hydrophobic compounds and are also involved in the regulation of many functions of the liver, cholangiocytes, and extrahepatic tissues, acting essentially as hormones. The biological effects are realized through variable membrane or nuclear receptors. Hepatic synthesis, intestinal modifications, intestinal peristalsis and permeability, and receptor activity can affect the quantitative and qualitative bile acids composition significantly leading to extrahepatic pathologies. The complexity of bile acids receptors and the effects of cross-activations makes interpretation of the results of the studies rather difficult. In spite, this is a very perspective direction for pharmacology.

Bile acids and salt-sensitive hypertension: a role of the gut-liver axis

Salt-sensitivity of blood pressure (SSBP) affects 50% of the hypertensive and 25% of the normotensive populations. Importantly, SSBP is associated with increased risk for mortality in both populations independent of blood pressure. Despite its deleterious effects, the pathogenesis of SSBP is not fully understood. Emerging evidence suggests a novel role of bile acids in salt-sensitive hypertension and that they may play a crucial role in regulating inflammation and fluid volume homeostasis. Mechanistic evidence implicates alterations in the gut microbiome, the epithelial sodium channel (ENaC), the farnesoid X receptor, and the G protein-coupled bile acid receptor TGR5 in bile acid-mediated effects on cardiovascular function. The mechanistic interplay between excess dietary sodium-induced alterations in the gut microbiome and immune cell activation, bile acid signaling, and whether such interplay may contribute to the etiology of SSBP is still yet to be defined. The main goal of this review is to discuss the potential role of bile acids in the pathogenesis of cardiovascular disease with a focus on salt-sensitive hypertension.

[Review of Research Progress in Biliary Substitutes]

Research and development of artificial biliary substitutes is an indispensable part of modern biliary surgery, bearing great clinical significance on the recovery of the normal functions of the biliary system. The implantation of artificial biliary substitutes may cause the blockage or stenosis of the biliary duct at the transplantation site, which is the most urgent problem in the research of artificial biliary substitutes. The fundamental cause of the problem is tissue hyperplasia caused by chronic inflammatory stimulation of artificial biliary substitutes. The regeneration of new bile duct tissue at the transplantation site can provide a solution to this problem. By looking at the literature from China and abroad, this paper reviewed the research and development of non-degradable artificial bile duct, degradable artificial bile duct and tissue-engineered artificial bile duct in order to provide reference for the further development of biliary replacements. Future studies should focus on the rapid formation of biliary epithelial layer on the tissue-engineered artificial biliary wall, the promotion of new biliary tissue formation, and the regulation of the degradation performance and mechanical properties of artificial biliary duct in order to fundamentally solve the problems encountered in the research of artificial biliary substitutes and accelerate the development of artificial biliary duct.

Mechanistic insights into the pathophysiology of cirrhotic cardiomyopathy

Myocardial dysfunction in end stage cirrhotic liver disease, termed cirrhotic cardiomyopathy, is a long known, but little understood comorbidity seen in ∼50% of adults and children who present for liver transplantation. Structural, functional, hemodynamic and electrocardiographic aberrations that occur in the heart as a direct consequence of a damaged liver, is associated with multi-organ failure and increased mortality and morbidity in patients undergoing surgical procedures such as porto-systemic shunt placement and liver transplantation. Despite its clinical significance and rapid advances in science and pharmacotherapy, there is yet no specific treatment for this disease. This may be due to a lack of understanding of the pathogenesis and mechanisms behind how a cirrhotic liver causes cardiac pathology. This review will focus specifically on insights into the molecular mechanisms that drive this liver-heart interaction. Deeper understanding of the etio-pathogenesis of cirrhotic cardiomyopathy will allow us to design and test treatments that can be targeted to prevent and/or reverse this co-morbid consequence of liver failure and improve health care delivery and outcomes in patients with cirrhosis.

Acute myocardial injury secondary to severe acute liver failure: A retrospective analysis supported by animal data

To investigate whether acute liver failure (ALF) leads to secondary acute myocardial injury, 100 ALF patients that were retrospectively identified in a single center based on ICD 10 codes and 8 rats from an experimental study that died early after bile duct ligation (BDL) were examined. Creatine kinase (CK), creatine kinase-MB isoenzyme (CKMB) and cardiac troponin-I (cTnI) were analyzed as markers of myocardial injury. For histological analysis, hematoxylin-eosin (HE), elastic Van Gieson (EVG), CD41 and myeloperoxidase were used to stain rat hearts. Major adverse cardiac events (MACEs) were a critical factor for mortality (p = 0.037) in human ALF. Deceased patients exhibited higher levels of CKMB than survivors (p = 0.023). CKMB was a predictor of mortality in ALF (p = 0.013). Animals that died early after BDL exhibited increased cTnI, CKMB, tumor necrosis factor α (TNFα) and interleukin-6 (IL-6) levels compared to controls (cTnI: p = 0.011, CKMB: p = 0.008, TNFα: p = 0.003, IL-6: p = 0.006). These animals showed perivascular lesions and wavy fibers, microthrombi and neutrophilic infiltration in the heart. MACEs are decisive for mortality in human ALF, and elevated CKMB values indicate that this might be due to structural myocardial damage. Accordingly, CKMB was found to have predictive value for mortality in ALF. The results are substantiated by data from a rat BDL model demonstrating diffuse myocardial injury.

Bile Acids, Liver Cirrhosis, and Extrahepatic Vascular Dysfunction

The bile acid pool with its individual bile acids (BA) is modulated in the enterohepatic circulation by the liver as the primary site of synthesis, the motility of the gallbladder and of the intestinal tract, as well as by bacterial enzymes in the intestine. The nuclear receptor farnesoid X receptor (FXR) and Gpbar1 (TGR5) are important set screws in this process. Bile acids have a vasodilatory effect, at least according to in vitro studies. The present review examines the question of the extent to which the increase in bile acids in plasma could be responsible for the hyperdynamic circulatory disturbance of liver cirrhosis and whether modulation of the bile acid pool, for example, via administration of ursodeoxycholic acid (UDCA) or via modulation of the dysbiosis present in liver cirrhosis could influence the hemodynamic disorder of liver cirrhosis. According to our analysis, the evidence for this is limited. Long-term studies on this question are lacking.

Diphlorethohydroxycarmalol Isolated from Ishige okamurae Exerts Vasodilatory Effects via Calcium Signaling and PI3K/Akt/eNOS Pathway

Nitric oxide (NO) is released by endothelial cells in the blood vessel wall to enhance vasodilation. Marine polyphenols are known to have protective effects against vascular dysfunction and hypertension. The present study is the first to investigate how diphlorethohydroxycarmalol (DPHC) isolated from Ishige okamurae affects calcium levels, resulting in enhanced vasodilation. We examined calcium modulation with the well-known receptors, acetylcholine receptor (AchR) and vascular endothelial growth factor 2 (VEGFR2), which are related to NO formation, and further confirmed the vasodilatory effect of DPHC. We confirmed that DPHC stimulated NO production by increasing calcium levels and endothelial nitric oxide synthase (eNOS) expression. DPHC affected AchR and VEGFR2 expression, thereby influencing transient calcium intake. Specific antagonists, atropine and SU5416, were used to verify our findings. Furthermore, based on the results of in vivo experiments, we treated Tg(flk:EGFP) transgenic zebrafish with DPHC to confirm its vasodilatory effect. In conclusion, the present study showed that DPHC modulated calcium transit through AchR and VEGFR2, increasing endothelial-dependent NO production. Thus, DPHC, a natural marine component, can efficiently ameliorate cardiovascular diseases by improving vascular function.

Non-alcoholic fatty liver disease: a metabolic burden promoting atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) has become the fastest growing chronic liver disease, with a prevalence of up to 25% worldwide. Individuals with NAFLD have a high risk of disease progression to cirrhosis, hepatocellular carcinoma (HCC), and liver failure. With the exception of intrahepatic burden, cardiovascular disease (CVD) and especially atherosclerosis (AS) are common complications of NAFLD. Furthermore, CVD is a major cause of death in NAFLD patients. Additionally, AS is a metabolic disorder highly associated with NAFLD, and individual NAFLD pathologies can greatly increase the risk of AS. It is increasingly clear that AS-associated endothelial cell damage, inflammatory cell activation, and smooth muscle cell proliferation are extensively impacted by NAFLD-induced systematic dyslipidemia, inflammation, oxidative stress, the production of hepatokines, and coagulations. In clinical trials, drug candidates for NAFLD management have displayed promising effects for the treatment of AS. In this review, we summarize the key molecular events and cellular factors contributing to the metabolic burden induced by NAFLD on AS, and discuss therapeutic strategies for the improvement of AS in individuals with NAFLD.

Allyl isothiocyanate (AITC) activates nonselective cation currents in human cardiac fibroblasts: possible involvement of TRPA1

The effects of allyl isothiocyanate (AITC), transient receptor potential ankyrin 1 (TRPA1) agonist, on cultured human cardiac fibroblasts were examined by measuring intracellular Ca²⁺ concentration [Ca²⁺]_i and whole-cell voltage clamp techniques. AITC (200 μM) increased Ca²⁺ entry in the presence of [Ca²⁺]_i. Ruthenium red (RR) (30 μM), and La³⁺ (0.5 mM), a general cation channel blocker, inhibited AITC-induced Ca²⁺ entry. Under the patch pipette filled with Cs⁺- and EGTA-solution, AITC induced the current of a reversal potential (Er) of approximately +0 mV. When extracellular Na⁺ ion was changed by NMDG⁺, the inward current activated by AITC was markedly reduced. La³⁺ and RR inhibited the AITC-induced current. The conventional RT-PCR analysis, Western blot, and immunocytochemical studies showed TRPA1 mRNA and protein expression. The present study shows the first evidence for functional Ca²⁺-permeable nonselective cation currents induced by AITC, possibly via TRPA1 in human cardiac fibroblast.

Overview of bile acid signaling in the cardiovascular system

Bile acids (BAs) are classically known to play a vital role in the metabolism of lipids and in absorption. It is now well established that BAs act as signaling molecules, activating different receptors (such as farnesoid X receptor, vitamin D receptor, Takeda G-protein-coupled receptor 5, sphingosine-1-phosphate, muscarinic receptors, and big potassium channels) and participating in the regulation of energy homeostasis and lipid and glucose metabolism. In addition, increased BAs can impair cardiovascular function in liver cirrhosis. Approximately 50% of patients with cirrhosis develop cirrhotic cardiomyopathy. Exposure to high concentrations of hydrophobic BAs has been shown to be related to adverse effects with respect to vascular tension, endothelial function, arrhythmias, coronary atherosclerotic heart disease, and heart failure. The BAs in the serum BA pool have relevant through their hydrophobicity, and the lipophilic BAs are more harmful to the heart. Interestingly, ursodeoxycholic acid is a hydrophilic BA, and it is used as a therapeutic drug to reverse and protect the harmful cardiac effects caused by hydrophobic elevated BAs. In order to elucidate the mechanism of BAs and cardiovascular function, abundant experiments have been conducted in vitro and in vivo. The aim of this review was to explore the mechanism of BAs in the cardiovascular system.

Modulation of endothelium-derived nitric oxide production and activity by taurine and taurine-conjugated bile acids

Taurine is a semiessential amino acid found at high concentrations in mammalian plasma and cells, where it regulates cellular functions such as ion flux, controls cell volume and serves as a substrate for conjugated bile acids (BAs). Exogenous administration of both taurine and taurine-conjugated BAs have also been implicated in the modulation of cardiovascular functions. This brief review summarizes the role of taurine and taurine-conjugated BAs in vascular relaxation through the modulation of endothelium-derived nitric oxide (NO). The effects of taurine on vascular health are controversial. However, in the presence of cardiometabolic risk factors, it has been proposed that taurine can increase vascular NO levels by increasing eNOS expression, eNOS phosphorylation on Ser1177, NO bioavailability, the level of antioxidative defense, and the l-arginine/NOS inhibitor asymmetric dimethylarginine (ADMA) ratio. The taurine-conjugated BA-mediated activation of Farnesoid X receptor (FXR), G protein-coupled BA receptor (TGR5) and/or muscarinic 3 receptor (M3) was also reported to increase vascular NO production. FXR activation increases eNOS expression and may reduce ADMA formation, while TGR5 increases mobilization of Ca²⁺ and phosphorylation of eNOS and Akt in endothelial cells. Furthermore, taurine and taurine-conjugated BAs might regulate NO synthesis and activity by enhancing H₂S generation. Several studies have demonstrated the beneficial effects of both taurine and taurine-conjugated BAs in reversing the endothelial dysfunction associated with diabetes, atherosclerosis, hypertension, obesity, malnutrition, and smoking. In addition, taurine-conjugated BAs have emerged as a potential treatment for portal hypertension. Despite these favorable findings, there is a need to further explore the mechanisms and signaling pathways underlying the endothelial effects of taurine and taurine-conjugated BAs. Here, we summarize the main findings regarding the effects of taurine and taurine-conjugated BAs on the endothelial dysfunction associated with altered NO metabolism in cardiovascular diseases.

Serum Metabonomics Analysis of Liver Failure Treated by Nonbioartificial Liver Support Systems

OBJECTIVE

To analyze the small molecular metabolic compounds of nonbioartificial liver for treatment of hepatic failure and make further efforts to study the clinical efficacy, mechanism of action, and pathogenesis of hepatic failure.

METHODS

52 patients who met the standard of artificial liver treatment for liver failure were enrolled; these patients included 6 cases of acute liver failure (11.54%), 3 cases of subacute liver failure (5.77%), acute-on-chronic liver failure in 10 cases (19.23%), and 33 cases of chronic liver failure (63.46%). Treatment modes included plasma exchange in 34 patients (65.38%), bilirubin adsorption in 9 patients (17.31%), and hemofiltration in 9 patients (17.31%). The clinical efficacy of artificial liver was assessed by monitoring the effects in the near future. Significant changes in metabolic compounds of liver failure in the treatment before and after artificial liver were screened by using Ultra-Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS). Related metabolic pathways were analyzed by MetaboAnalyst.

RESULTS

After artificial liver treatment, the liver function and coagulation function of liver failure patients were significantly improved (P < 0.01), the Meld score was lower than that before treatment, and the difference was statistically significant (P < 0.05). Serum metabolomics identified 29 small metabolic compounds and 12 metabolic pathways with variable projection importance (VIP) greater than 1 before and after artificial liver treatment. There were 11 metabolic compounds of VIP over 1 and 7 metabolic pathways in the different modes of artificial liver treatment for chronic liver failure. Among them, bile acid metabolism, fatty acid metabolism, and amino acid metabolism are the main sources.

CONCLUSION

Artificial liver treatment can effectively improve liver function and blood coagulation function and Meld score, clinical symptoms and signs in patients with liver failure; the curative effect of artificial liver was verified, which reflected the clinical value of artificial liver in the treatment of liver failure. Artificial liver treatment of liver failure on fatty acids and primary bile acid synthesis pathway was the most significant. The difference of fatty acid, primary bile acid synthesis pathway, and phenylalanine metabolic pathway in different artificial liver patterns of chronic liver failure was the most significant. This provides a new basis for understanding the mechanism of hepatic failure and the mechanism of liver failure by artificial liver treatment.

Heart and bile acids - Clinical consequences of altered bile acid metabolism

Cardiac dysfunction has an increased prevalence in diseases complicated by liver cirrhosis such as primary biliary cholangitis and primary sclerosing cholangitis. This observation has led to research into the association between abnormalities in bile acid metabolism and cardiac pathology. Approximately 50% of liver cirrhosis cases develop cirrhotic cardiomyopathy. Bile acids are directly implicated in this, causing QT interval prolongation, cardiac hypertrophy, cardiomyocyte apoptosis and abnormal haemodynamics of the heart. Elevated maternal serum bile acids in intrahepatic cholestasis of pregnancy, a disorder which causes an impaired feto-maternal bile acid gradient, have been associated with fatal fetal arrhythmias. The hydrophobicity of individual bile acids in the serum bile acid pool is of relevance, with relatively lipophilic bile acids having a more harmful effect on the heart. Ursodeoxycholic acid can reverse or protect against these detrimental cardiac effects of elevated bile acids.

Bile acids and cardiovascular function in cirrhosis

Cirrhotic cardiomyopathy and the hyperdynamic syndrome are clinically important complications of cirrhosis, but their exact pathogenesis is still partly unknown. Experimental models have proven the cardiotoxic effects of bile acids and recent studies of their varied receptor-mediated functions offer new insight into their involvement in cardiovascular dysfunction in cirrhosis. Bile acid receptors such as farnesoid X-activated receptor and TGR5 are currently under investigation as potential therapeutic targets in a variety of pathological conditions. These receptors have also recently been identified in cardiomyocytes, vascular endothelial cells and smooth muscle cells where they seem to play an important role in cellular metabolism. Chronic cholestasis leading to abnormal levels of circulating bile acids alters the normal signalling pathways and contributes to the development of profound cardiovascular disturbances. This review summarizes the evidence regarding the role of bile acids and their receptors in the generation of cardiovascular dysfunction in cirrhosis.

Decoding the vasoregulatory activities of bile acid-activated receptors in systemic and portal circulation: role of gaseous mediators

Bile acids are end products of cholesterol metabolism generated in the liver and released in the intestine. Primary and secondary bile acids are the result of the symbiotic relation between the host and intestinal microbiota. In addition to their role in nutrient absorption, bile acids are increasingly recognized as regulatory signals that exert their function beyond the intestine by activating a network of membrane and nuclear receptors. The best characterized of these bile acid-activated receptors, GPBAR1 (also known as TGR5) and the farnesosid-X-receptor (FXR), have also been detected in the vascular system and their activation mediates the vasodilatory effects of bile acids in the systemic and splanchnic circulation. GPBAR1, is a G protein-coupled receptor, that is preferentially activated by lithocholic acid (LCA) a secondary bile acid. GPBAR1 is expressed in endothelial cells and liver sinusoidal cells (LSECs) and responds to LCA by regulating the expression of both endothelial nitric oxide synthase (eNOS) and cystathionine-γ-lyase (CSE), an enzyme involved in generation of hydrogen sulfide (H₂S). Activation of CSE by GPBAR1 ligands in LSECs is due to genomic and nongenomic effects, involves protein phosphorylation, and leads to release of H₂S. Despite that species-specific effects have been described, vasodilation caused by GPBAR1 ligands in the liver microcirculation and aortic rings is abrogated by inhibition of CSE but not by eNOS inhibitor. Vasodilation caused by GPBAR1 (and FXR) ligands also involves large conductance calcium-activated potassium channels likely acting downstream to H₂S. The identification of GPBAR1 as a vasodilatory receptor is of relevance in the treatment of complex disorders including metabolic syndrome-associated diseases, liver steatohepatitis, and portal hypertension.

The bile acid TUDCA increases glucose-induced insulin secretion via the cAMP/PKA pathway in pancreatic beta cells

OBJECTIVE

While bile acids are important for the digestion process, they also act as signaling molecules in many tissues, including the endocrine pancreas, which expresses specific bile acid receptors that regulate several cell functions. In this study, we investigated the effects of the conjugated bile acid TUDCA on glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells.

METHODS

Pancreatic islets were isolated from 90-day-old male mice. Insulin secretion was measured by radioimmunoassay, protein phosphorylation by western blot, Ca(2+) signals by fluorescence microscopy and ATP-dependent K(+) (KATP) channels by electrophysiology.

RESULTS

TUDCA dose-dependently increased GSIS in fresh islets at stimulatory glucose concentrations but remained without effect at low glucose levels. This effect was not associated with changes in glucose metabolism, Ca(2+) signals or KATP channel activity; however, it was lost in the presence of a cAMP competitor or a PKA inhibitor. Additionally, PKA and CREB phosphorylation were observed after 1-hour incubation with TUDCA. The potentiation of GSIS was blunted by the Gα stimulatory, G protein subunit-specific inhibitor NF449 and mimicked by the specific TGR5 agonist INT-777, pointing to the involvement of the bile acid G protein-coupled receptor TGR5.

CONCLUSION

Our data indicate that TUDCA potentiates GSIS through the cAMP/PKA pathway.

Effects of methylglyoxal on human cardiac fibroblast: roles of transient receptor potential ankyrin 1 (TRPA1) channels

Cardiac fibroblasts contribute to the pathogenesis of cardiac remodeling. Methylglyoxal (MG) is an endogenous carbonyl compound produced under hyperglycemic conditions, which may play a role in the development of pathophysiological conditions including diabetic cardiomyopathy. However, the mechanism by which this occurs and the molecular targets of MG are unclear. We investigated the effects of MG on Ca(2+) signals, its underlying mechanism, and cell cycle progression/cell differentiation in human cardiac fibroblasts. The conventional and quantitative real-time RT-PCR, Western blot, immunocytochemical analysis, and intracellular Ca(2+) concentration [Ca(2+)]i measurement were applied. Cell cycle progression was assessed using the fluorescence activated cell sorting. MG induced Ca(2+) entry concentration dependently. Ruthenium red (RR), a general cation channel blocker, and HC030031, a selective transient receptor potential ankyrin 1 (TRPA1) antagonist, inhibited MG-induced Ca(2+) entry. Treatment with aminoguanidine, a MG scavenger, also inhibited it. Allyl isothiocyanate, a selective TRPA1 agonist, increased Ca(2+) entry. The use of small interfering RNA to knock down TRPA1 reduced the MG-induced Ca(2+) entry as well as TRPA1 mRNA expression. The quantitative real-time RT-PCR analysis showed the prominent existence of TRPA1 mRNA. Expression of TRPA1 protein was confirmed by Western blotting and immunocytochemical analyses. MG promoted cell cycle progression from G0/G1 to S/G2/M, which was suppressed by HC030031 or RR. MG also enhanced α-smooth muscle actin expression. The present results suggest that methylglyoxal activates TRPA1 and promotes cell cycle progression and differentiation in human cardiac fibroblasts. MG might participate the development of pathophysiological conditions including diabetic cardiomyopathy via activation of TRPA1.

Obstructive jaundice and perioperative management

The causes of obstructive jaundice are varied, but it is most commonly due to choledocholithiasis; benign strictures of the biliary tract; pancreaticobiliary malignancies; and metastatic disease. Surgery in patients with obstructive jaundice is generally considered to be associated with a higher incidence of complications and mortality. Therefore, it poses a considerable challenge to the anesthesiologist, surgeons, and the intensive care team. However, appropriate preoperative evaluation and optimization can greatly contribute to a favorable outcome for perioperative jaundiced patients. This article outlines the association between obstructive jaundice and perioperative management, and reviews the clinical and experimental studies that have contributed to our knowledge of the underlying pathophysiologic mechanisms. Pathophysiology caused by obstructive jaundice involving coagulopathies, infection, renal dysfunction, and other adverse events should be fully assessed and reversed preoperatively. The depressed cardiovascular effects of obstructive jaundice are worth noticing because it has complicated mechanisms and needs to be further explored. Alterations of anesthesia-related drugs induced by obstructive jaundice are varied and clinicians should be aware of the possible need for a decrease in the anesthetic dose. Recommendations concerning the perioperative management of the patients with obstructive jaundice including preoperative biliary drainage, anti-infection, nutrition support, coagulation reversal, cardiovascular evaluation, perioperative fluid therapy, and hemodynamic optimization should be taken.

G protein-coupled bile acid receptor 1 stimulation mediates arterial vasodilation through a K(Ca)1.1 (BK(Ca))-dependent mechanism

Bile acids (BAs) and BA receptors, including G protein-coupled bile acid receptor 1 (GPBAR1), represent novel targets for the treatment of metabolic and inflammatory disorders. However, BAs elicit myriad effects on cardiovascular function, although this has not been specifically ascribed to GPBAR1. This study was designed to test whether stimulation of GPBAR1 elicits effects on cardiovascular function that are mechanism based that can be identified in acute ex vivo and in vivo cardiovascular models, to delineate whether effects were due to pathways known to be modulated by BAs, and to establish whether a therapeutic window between in vivo cardiovascular liabilities and on-target efficacy could be defined. The results demonstrated that the infusion of three structurally diverse and selective GPBAR1 agonists produced marked reductions in vascular tone and blood pressure in dog, but not in rat, as well as reflex tachycardia and a positive inotropic response, effects that manifested in an enhanced cardiac output. Changes in cardiovascular function were unrelated to modulation of the levothyroxine/thyroxine axis and were nitric oxide independent. A direct effect on vascular tone was confirmed in dog isolated vascular rings, whereby concentration-dependent decreases in tension that were tightly correlated with reductions in vascular tone observed in vivo and were blocked by iberiotoxin. Compound concentrations in which cardiovascular effects occurred, both ex vivo and in vivo, could not be separated from those necessary for modulation of GPBAR1-mediated efficacy, resulting in project termination. These results are the first to clearly demonstrate direct and potent peripheral arterial vasodilation due to GPBAR1 stimulation in vivo through activation of large conductance Ca(2+) activated potassium channel K(Ca)1.1.

The involvement of endoplasmic reticulum stress in bile acid-induced hepatocellular injury

Secondary bile acids produced by enteric bacteria accumulate to high levels in the enterohepatic circulation and may contribute to the pathogenesis of hepatocellular injury. Relative hydrophobicity has been suggested to be an important determinant of the biological properties of these compounds, although the mechanism by which bile acids induce pathogenesis is not fully understood. On the other hand, endoplasmic reticulum stress has been shown to be involved in the induction and development of various pathogenic conditions. In this report, we demonstrated that the intensities of cytotoxicity and endoplasmic reticulum stress in HepG2 cells triggered by the bile acids tested were largely dependent on their hydrophobicity. The activation of caspase-3 and DNA fragmentation by treatment with chenodeoxycholic acid showed the contribution of apoptosis to cytotoxicity. Increases in intracellular calcium levels and the generation of reactive oxygen species stimulated by treatment with chenodeoxycholic acid contributed to endoplasmic reticulum stress. Bile acids also induced transforming growth factor-β, a potent profibrogenic factor, which is known to induce hepatocyte apoptosis and ultimately liver fibrosis. In conclusion, our study demonstrated that bile acids induced endoplasmic reticulum stress, which in turn stimulated apoptosis in HepG2 cells, in a hydrophobicity-dependent manner.

Roles of transient receptor potential canonical (TRPC) channels and reverse-mode Na+/Ca2+ exchanger on cell proliferation in human cardiac fibroblasts: effects of transforming growth factor β1

Expression of transient receptor potential canonical channels (TRPC) and the effects of transforming growth factor-β1 (TGF-β1) on Ca2+ signals and fibroblast proliferation were investigated in human cardiac fibroblasts. The conventional and quantitative real-time RT-PCR, western blot, immunocytochemical analysis, and intracellular Ca2+ concentration [Ca2+]i measurement were applied. Cell proliferation and cell cycle progression were assessed using MTT assays and fluorescence activated cell sorting. Human cardiac fibroblasts have the expression of TRPC1,3,4,6 mRNA and proteins. 1-oleoyl-2-acetyl-sn-glycerol (OAG) and thapsigargin induced extracellular Ca(2+)-mediated [Ca2+]i rise. siRNA for knock down of TRPC6 reduced OAG-induced Ca2+ entry. Hyperforin as well as angiotensin II (Ang II) induced Ca2+ entry. KB-R7943, a reverse-mode Na+/Ca2+ exchanger (NCX) inhibitor, and/or replacement of Na+ with NMDG+ inhibited thapsigargin-, OAG- and Ang II-induced Ca2+ entry. Treatment with TGF-β1 increased thapsigargin-, OAG- and Ang II-induced Ca2+ entry with an enhancement of TRPC1,6 protein expression, suppressed by KB-R7943. TGF-β1 and AngII promoted cell cycle progression from G0/G1 to S/G2/M and cell proliferation. A decrease of the extracellular Ca2+ and KB-R7943 suppressed it. Human cardiac fibroblasts contain several TRPC-mediated Ca2+ influx pathways, which activate the reverse-mode NCX. TGF-β1 enhances the Ca2+ influx pathways requiring Ca2+ signals for its effect on fibroblast proliferation.

Effects of deoxycholylglycine, a conjugated secondary bile acid, on myogenic tone and agonist-induced contraction in rat resistance arteries

BACKGROUND

Bile acids (BAs) regulate cardiovascular function via diverse mechanisms. Although in both health and disease serum glycine-conjugated BAs are more abundant than taurine-conjugated BAs, their effects on myogenic tone (MT), a key determinant of systemic vascular resistance (SVR), have not been examined.

METHODOLOGY/PRINCIPAL FINDINGS

Fourth-order mesenteric arteries (170-250 µm) isolated from Sprague-Dawley rats were pressurized at 70 mmHg and allowed to develop spontaneous constriction, i.e., MT. Deoxycholylglycine (DCG; 0.1-100 µM), a glycine-conjugated major secondary BA, induced reversible, concentration-dependent reduction of MT that was similar in endothelium-intact and -denuded arteries. DCG reduced the myogenic response to stepwise increase in pressure (20 to 100 mmHg). Neither atropine nor the combination of L-NAME (a NOS inhibitor) plus indomethacin altered DCG-mediated reduction of MT. K(+) channel blockade with glibenclamide (K(ATP)), 4-aminopyradine (K(V)), BaCl(2) (K(IR)) or tetraethylammonium (TEA, K(Ca)) were also ineffective. In Fluo-2-loaded arteries, DCG markedly reduced vascular smooth muscle cell (VSM) Ca(2+) fluorescence (∼50%). In arteries incubated with DCG, physiological salt solution (PSS) with high Ca(2+) (4 mM) restored myogenic response. DCG reduced vascular tone and VSM cytoplasmic Ca(2+) responses (∼50%) of phenylephrine (PE)- and Ang II-treated arteries, but did not affect KCl-induced vasoconstriction.

CONCLUSION

In rat mesenteric resistance arteries DCG reduces pressure- and agonist-induced vasoconstriction and VSM cytoplasmic Ca(2+) responses, independent of muscarinic receptor, NO or K(+) channel activation. We conclude that BAs alter vasomotor responses, an effect favoring reduced SVR. These findings are likely pertinent to vascular dysfunction in cirrhosis and other conditions associated with elevated serum BAs.

Bile acids regulate cardiovascular function

Research over the last decade has uncovered roles for bile acids (BAs) that extend beyond their traditional functions in regulating lipid digestion and cholesterol metabolism. BAs are now recognized as signaling molecules that interact with both plasma membrane and nuclear receptors. Emerging evidence indicates that by interacting with these receptors, BAs regulate their own synthesis, glucose and energy homeostasis, and other important physiological events. Herein, we provide a comprehensive review of the actions of BAs on cardiovascular function. In the heart and the systemic circulation, BAs interact with plasma membrane G-protein-coupled receptors, for example, TGR5 and muscarinic receptors, and nuclear receptors, for example, the farnesoid (FXR) and pregnane (PXR) xenobiotic receptors. BA receptors are expressed in cardiovascular tissue, however, the mechanisms underlying BA-mediated regulation of cardiovascular function remain poorly understood. BAs reduce heart rate by regulating channel conductance and calcium dynamics in sino-atrial and ventricular cardiomyocytes and regulate vascular tone via both endothelium-dependent and -independent mechanisms. End-stage liver disease, obstructive jaundice, and intrahepatic cholestasis of pregnancy are prominent conditions in which elevated serum BAs alter vascular dynamics. This review focuses on BAs as newly recognized signaling molecules that modulate cardiovascular function.

Regulation of CDX2 expression in esophageal adenocarcinoma

Reflux of acidic gastric contents and bile acids into the lower esophagus has been identified to have a central role in esophageal malignancy and is reported to upregulate caudal-related homologue 2 (CDX2), a regulatory gene involved in embryonic development and axial patterning of the alimentary tract. The aim of this study was to characterize the expression of CDX2 in a well-defined series of human esophageal tissues, comprising reflux-induced esophagitis, premalignant Barrett esophagus (BE), and primary esophageal adenocarcinoma (EADC). To explore potential molecular regulatory mechanisms, we also studied the expression of beta-catenin, SOX9, and CDX2 promoter methylation in esophageal tissues, in addition to the effect of bile acids and nitric oxide (NO) on CDX2 expression in the normal human esophageal cell line Het1A. Relative to matched normal esophageal epithelia, CDX2 was overexpressed in esophagitis (37% for RNA; cytoplasmic immunoreactivity in 48% of tissues), a high proportion (91%) of BE tissues, and in EADC (57% for RNA; cell nuclear immunopositivity in 80%). An association with beta-catenin expression was seen, but not with SOX9 or CDX2 promoter methylation. In Het1A cells, CDX2 was upregulated following exposure to bile acids and NO, alone and in combination. These results further implicate CDX2 and beta-catenin in the molecular pathogenesis of human EADC. The observed synergistic effect of NO on the efficacy of bile acid-induction of CDX2 suggests a novel role for NO in modulating the development of the Barrett phenotype and esophageal adenocarcinogenesis.

Ca2+-dependent K+ efflux regulates deoxycholate-induced apoptosis of BHK-21 and Caco-2 cells

BACKGROUND & AIMS

Deoxycholate (DC) has proapoptotic and tumorigenic effects in different cell types of the gastrointestinal tract. Exposure of BHK-21 (stromal) cells to DC induces Ca(2+) entry at the plasma membrane, which affects intracellular Ca(2+) signaling. We assessed whether DC-induced increases in [Ca(2+)] can impinge on plasma membrane properties (eg, ionic conductances) involved in cell apoptosis.

METHODS

Single- and double-barreled microelectrodes were used to measure membrane potential (V(m)) and extracellular [K(+)] in BHK-21 fibroblasts and Caco-2 colon carcinoma cells. Apoptosis was assessed by Hoechst labeling, propidium iodide staining, and caspase-3 and caspase-7 assays.

RESULTS

DC-induced cell membrane hyperpolarization was directly measured with intracellular microelectrodes in both cell lines. Diverse Ca(2+) mobilizing agents, such as membrane receptor agonists, an inhibitor of the sarco/endoplasmic reticulum Ca(2+) adenosine triphosphatase and a Ca(2+) ionophore, also induced increases in V(m). Removal of extracellular Ca(2+) reduced the agonist- and DC-induced membrane hyperpolarization by approximately 15% and 60%, respectively. These findings indicate a prominent role for Ca(2+) entry at the plasma membrane in the action of this bile salt. Blockade of Ca(2+)-activated K(+) conductances by charybdotoxin and apamin reduced DC-induced hyperpolarization by 75% and 64% in BHK-21 and Caco-2 cells, respectively. These inhibitors also reduced the DC-induced increase in extracellular [K(+)] by 75% and cell apoptosis by approximately 50% in both cell lines.

CONCLUSIONS

Ca(2+)-dependent K(+) conductance is an important regulator of DC-induced apoptosis in stromal and colon cancer cells.

Embryonic stem cell-derived cardiomyocytes as a model to study fetal arrhythmia related to maternal disease

Embryonic stem cell-derived cardiomyocytes (ESC-CM) have many of the phenotypic properties of authentic cardiomyocytes, and great interest has been shown in their possibilities for modelling human disease. Obstetric cholestasis affects 1 in 200 pregnant women in the United Kingdom. It is characterized by raised serum bile acids and complicated by premature delivery and unexplained fetal death at late gestation. It has been suggested that the fetal death is caused by the enhanced arrhythmogenic effect of bile acids in the fetal heart, and shown that neonatal susceptibility to bile acid-induced arrhythmia is lost in the adult rat cardiomyocyte. However, the mechanisms of the observed bile acid effects are not fully understood and their in vivo study in human beings is difficult. Here we use ESC-CM from both human and mouse ESCs to test our proposal that immature cardiomyocytes are more susceptible to the effect of raised bile acids than mature ones. We show that early ESC-CM exhibit bile acid-induced disruption of rhythm, depression of contraction and desynchronization of cell coupling. In both species the ESC-CM become resistant to these arrhythmias as the cells mature, and this develops in line with the respective gestational periods of mouse and human. This represents the first demonstration of the use of ESC-CM as a model system for human cardiac pathology, and opens the way for both investigation of mechanisms and a high throughput screen for drug discovery.

Sodium deoxycholate causes nitric oxide mediated DNA damage in oesophageal cells

Patients with chronic gastro-oesophageal reflux disease experience the reflux of acid and bile into the distal oesophagus. The secondary bile salt sodium deoxycholate (NDC) is implicated in the induction of mucosal injury during reflux episodes. This study hypothesized that NDC damages DNA in oesophageal cells by an oxidative mechanism. In the oesophageal cell line HET1-A, increased production of nitric oxide (NO) was measured in NDC-treated cells. Protection from DNA strand breaks induced by NDC (10 microm) was observed in cells coincubated with the nitric oxide scavenger C-PTIO (p<0.012) or pre-incubated with the NO synthase inhibitor L-NAME (p<0.009) or the NFkappaB inhibitor, TPCK (p<0.036). Collectively these data implicate the involvement of NFkappaB and nitric oxide synthase in the DNA damage induced by NDC in oesophageal cells. In conclusion, NDC-driven NO production may play an important role in inducing DNA damage during episodes of gastro-oesophageal reflux and thereby contribute to reflux-related carcinogenesis.

The future treatment of portal hypertension

Increased understanding of the hyperdynamic circulation syndrome has resulted in novel therapeutic approaches, some of which have already reached clinical practice. Central to the hyperdynamic circulation syndrome is an imbalance between the increase in different vasodilators (foremost among which is nitric oxide) and the compensatory increase in vasoconstrictors--usually accompanied by a blunted response. This chapter discusses the role of endothelin in the pathogenesis of the syndrome and in future treatment approaches. A relatively new area of research in this field is the role of infection and inflammation in the initiation and maintenance of the hyperdynamic circulation syndrome. The use of antibiotics in the setting of acute variceal bleeding is standard practice. Studies have suggested that chronic manipulation of the intestinal flora could have beneficial effects in the treatment of portal hypertension. The bile salts are another novel and interesting target. Although their vasoactive properties have been known for some time, recent data demonstrate that their effects could be central in the pathogenesis of the hyperdynamic circulation syndrome, and that manipulation of the composition of the bile acid pool could be a therapeutic approach to portal hypertension. Finally, hypoxia and angiogenesis play a role in the development of portal hypertension and the formation of collaterals. This role needs to be further defined but it appears likely that this phenomenon is yet another target for therapeutic intervention.

Comparative effects of azelnidipine and other Ca2+-channel blockers on the induction of inducible nitric oxide synthase in vascular smooth muscle cells

Overproduction of nitric oxide by inducible nitric oxide synthase contributes to the progression of cardiovascular disease. We investigated the effects of azelnidipine and other Ca2+-channel blockers on nitric oxide production by cultured aortic smooth muscle cells isolated from Wistar rats and human umbilical vein endothelial cells (HUVECs), using the Griess reaction and oxyhemoglobin method. Release of lactic dehydrogenase (LDH) was measured to evaluate cell damage, and immunohistochemistry was performed to examine the expression of inducible nitric oxide synthase and nitrotyrosine protein. Azelnidipine and other Ca2+-channel blockers inhibited the release of nitric oxide induced by lipopolysaccharide plus interferon-gamma. Azelnidipine inhibited it most potently among the Ca2+-channel blockers tested (azelnidipine, amlodipine, nifedipine, diltiazem, verapamil, and nicardipine) at a concentration of 10 microM. Longer stimulation with these agents induced the expression of inducible nitric oxide synthase and nitrotyrosine, with an increase of lactic dehydrogenase release, whereas azelnidipine suppressed these changes. In human umbilical vein endothelial cells, azelnidipine enhanced basal nitric oxide production by endothelial nitric oxide synthase. In conclusion, azelnidipine potently inhibited the induction of inducible nitric oxide synthase and then nitric oxide production in vascular smooth muscle cells, while enhancing constitutive nitric oxide production by endothelial cells. Azelnidipine may inhibit nitrotyrosine expression and cell damage caused by overproduction of nitric oxide, suggesting a mechanism for its cardiovascular protective effect.

Amiodarone and N-Desethylamiodarone Enhance Endothelial Nitric Oxide Production in Human Endothelial Cells

Amiodarone (AM) is a potent vasodilator and exhibits diverse cardiovascular protective effects in vivo, but their underlying mechanisms remain unsettled. We investigated the effects of AM and N-desethylamiodarone (DEA), the major metabolite of AM, on endothelial nitric oxide (NO) production using cultured human umbilical vein endothelial cells (HUVECs). The release of NO was evaluated as measured by nitrite, a stable metabolite of NO, using the Griess reaction and also measured directly by a NO-selective electrode. The expression of each nitric oxide synthase (NOS) mRNA was examined by reverse transcriptase-polymerase chain reaction (RT-PCR), and the effects of AM on eNOS mRNA expression were studied by quantitative real-time RT-PCR. AM and DEA (1-30 microM) enhanced NO production in a concentration-dependent manner. DEA was capable of producing more NO than AM. L-NAME, a nonselective NOS inhibitor, EGTA, a Ca(2+)-chelating agent, and nickel, a nonspecific Ca(2+) blocker, all inhibited AM-induced NO production. However, LY294002, an Akt pathway inhibitor and SB202190, a MAP kinase inhibitor, did not significantly suppress the production. In RT-PCR analysis, only eNOS mRNA was detected. Treatment with AM for 4 hours did not show a significant increase in the expression of eNOS mRNA. AM lower than 30 microM did not induce apoptosis, net cell loss, or LDH release from cells. The present study provides the first evidence that therapeutic concentrations of AM and DEA enhance eNOS-mediated NO production without any toxic or apoptotic effects. This mechanism may underlie the cardiovascular protective effects of AM and its metabolite observed in a clinical setting.

Inhibition of rat vascular smooth muscle cell proliferation by extract of Ligusticum chuanxiong and Angelica sinensis

Ligusticum chuanxiong (LC) and Angelica sinensis (AS) have been widely used as traditional Chinese medicine to treat some pathological settings such as atherosclerosis and hypertension. The aim of this paper is to determine the effects of the extract of LC and AS (ELCAS) on serum-induced vascular smooth muscle cell (VSMC) proliferation, cell cycle and nitric oxide production. The results show that ELCAS significantly inhibited proliferation and protein synthesis of VSMC in a dose and time dependent manner. The cell population assessed by flow cytometry in the G(0)/G(1) phase increased 74% versus 79.8%, concomitant with a decrease in the S phase, 7.4% versus 4.2%, for control versus ELCAS (300 microg/ml). On the other hand, ELCAS significantly increased nitric oxide production of VSMC. The data suggest that ELCAS markedly inhibited VSMC proliferation by arresting G(1) to S progression, which may be associated with nitric oxide production.

Deoxycholyltaurine-induced vasodilation of rodent aorta is nitric oxide- and muscarinic M3 receptor-dependent

Emerging evidence indicates that some secondary bile acids interact functionally with muscarinic cholinergic receptors. Using thoracic aortic rings prepared from rats and mice, we examined the mechanism of deoxycholyltaurine-induced vasorelaxation. Increasing concentrations of both acetylcholine (1 nM to 0.1 mM) and deoxycholyltaurine (0.1 microM to 1 mM) stimulated relaxation of phenylephrine-constricted rings prepared from rat thoracic aortae. These effects were reduced by endothelial denudation and by treatment with an inhibitor of nitric oxide formation and with a synthetic acetylcholine:bile acid hybrid that acts as a muscarinic receptor antagonist. Likewise, both acetylcholine (1 nM to 0.1 mM) and deoxycholyltaurine (0.1 microM to 0.1 mM) stimulated relaxation of phenylephrine-constricted rings prepared from mouse thoracic aortae. These effects were reduced by endothelial denudation, addition of an inhibitor of nitric oxide formation, and by muscarinic M(3) receptor knockout. We conclude that the systemic vasodilatory actions of deoxycholyltaurine are mediated in part by a nitric oxide-, muscarinic M(3) receptor-dependent mechanism. In advanced liver disease, interaction of serum bile acids with endothelial muscarinic receptors may explain nitric oxide overproduction in the systemic circulation and resulting peripheral arterial vasodilation.

Ursodeoxycholic acid inhibits endothelin-1 production in human vascular endothelial cells

Endothelin-1 is known to be implicated in the pathogenesis of hepatobiliary diseases such as cirrhosis, especially in portal hypertension. This study aimed to investigate the effects of ursodeoxycholic acid on endothelin-1 production in human endothelial cells. The effects of ursodeoxycholic acid and its conjugates (tauroursodeoxycholic and glycoursodeoxycholic acids) on endothelin-1 production as well as nitric oxide (NO) in human umbilical vein endothelial cells (HUVECs) were examined. The production of endothelin-1 and nitric oxide in culture medium was measured using enzyme-linked immunosorbent assay (ELISA) and the Griess method, respectively. Endothelin-1 and endothelial nitric oxide synthase (eNOS) mRNA expression were investigated by real-time quantitative reverse transcriptase/polymerase chain reaction (RT-PCR). Ursodeoxycholic acid (30-1000 microM) inhibited endothelin-1 production in a concentration-dependent manner, and ursodeoxycholic acid at concentrations higher than 300 microM increased nitric oxide production in culture medium. The conjugates of ursodeoxycholic acid also increased nitric oxide production and decreased endothelin-1 production, which was less effective than ursodeoxycholic acid. N-nitro-L-arginine-mythel-ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, suppressed the ursodeoxycholic acid-induced nitric oxide production, but it did not antagonize the inhibitory effects of ursodeoxycholic acid on endothelin-1 production. Ursodeoxycholic acid also induced a concentration-dependent decrease in endothelin-1 mRNA expression without significant changes in eNOS mRNA expression. These results provide novel evidence that ursodeoxycholic acid inhibits endothelin-1 production in human endothelial cells, but nitric oxide is not responsible for the inhibitory effect of ursodeoxycholic acid on endothelin-1. Thus, ursodeoxycholic acid therapy may prevent the development of several pathogenesis such as portal hypertension observed in patients with cirrhosis due to the improvement of endothelial function.

Inhibitory effects of carvedilol on calcium channels in vascular smooth muscle cells

Carvedilol has hypotensive effects and inhibits agonist-induced cell proliferation of vascular smooth muscle and then prevents vascular remodeling. However, the basic mechanisms have not been clarified. We examined the effects of carvedilol on [Ca2+]i mobilization and voltage-dependent L-type Ca2+ current (ICa.L) in vascular smooth muscle cells, and compared them with metoprolol. [Ca2+]i was measured using fura-2 AM and patch clamp techniques in rat embryonic aortic smooth muscle cells (A7r5). In the presence of extracellular Ca2+, vasopressin and endothelin-1 increased [Ca2+]i due first to the Ca2+ release from store sites, and subsequently Ca2+ entry. Carvedilol did not inhibit the Ca2+ release, but significantly suppressed the sustained rise due to Ca2+ entry concentration-dependently. Nilfedipine and nicardipine (10 microM) partly inhibited the sustained rise, but carvedilol inhibited it more effectively than the Ca2+ channel blockers. Under voltage clamp conditions, carvedilol (0.2-10 microM) reversibly inhibited the ICa.L concentration-dependently without any changes in the current-voltage relationships of ICa.L. Carvedilol shifted the steady-state inactivation for ICa.L to more negative potentials and inhibited ICa.L in a voltage-dependent manner. In addition, carvedilol did not inhibit Ca2+ release from store sites induced by thapsigargin, but significantly inhibited the sustained rise due to capacitative Ca2+ entry unrelated to ICa.L. In contrast, metoprolol did not mimic these effects of carvedilol. These results provide evidence that carvedilol inhibits ICa.L and may also inhibit the channels for agonist (vasopressin and endothelin-1)-induced Ca2+ entry in vascular smooth muscle cells, which might contribute to the vasorelaxing and antiproliferative effects of carvedilol.

Inhibitory effects of ursodeoxycholic acid on the induction of nitric oxide synthase in vascular smooth muscle cells

The expression of inducible nitric oxide synthase (iNOS) and the resultant increased nitric oxide production are associated with endotoxemia and atherosclerotic lesions observed in transplant hearts or balloon-injured artery. Ursodeoxycholic acid has been shown to have cardiovascular protective effects, such as inhibition of the development of transplant arteriosclerosis, but its mechanism remains unclear. Here, we investigated the effects of ursodeoxycholic acid on nitric oxide production and the expression of iNOS in vascular smooth muscle cells isolated from adult rat aorta and rabbit coronary artery. Nitrite released from cells in the culture medium was measured with the Griess reaction. iNOS mRNA and protein were measured by Northern and Western blot analyses. Treatment with ursodeoxycholic acid (30-1000 microM) significantly inhibited lipopolysaccharide plus interferon-gamma-induced nitric oxide production in a concentration-dependent manner, but ursodeoxycholic acid showed only small inhibitory effects on nitric oxide production that had already been induced by lipopolysaccharide plus interferon-gamma. Ursodeoxycholic acid by itself did not affect basal nitric oxide production. Ursodeoxycholic acid also suppressed lipopolysaccharide plus interferon-gamma-induced expression of iNOS mRNA and protein. Ursodeoxycholic acid had the most potent inhibitory effect among various kinds of bile acids examined, i.e. chenodeoxycholic acid, deoxycholic acid, cholic acid and conjugated bile acids such as tauroursodeoxycholic acid. These results suggest that ursodeoxycholic acid inhibits the induction of iNOS and then nitric oxide production in aortic and coronary artery smooth muscle cells, suggesting a possible mechanism for the cardiovascular protective effect of ursodeoxycholic acid under various pathophysiological conditions such as endotoxemia and atherosclerosis.

Increase in renal glutathione in cholestatic liver disease is due to a direct effect of bile acids

Hepatic synthesis and plasma levels of glutathione are markedly decreased in chronic liver disease. Because glutathione turnover is highest in kidneys, we examined whether changes in kidney glutathione occur in chronic cholestasis and whether they are related to kidney dysfunction in liver disease. Kidney and plasma GSH and GSSG were measured 1) in bile duct-ligated (BDL) rats; 2) in healthy rats after bile acid loading to mimic cholestasis; and 3) after irreversible inhibition of glutathione synthetase with buthionine-sulfoximine (BSO), where glutathione consumption, urinary volume, and sodium excretion were also estimated. In addition, gamma-glutamylcysteine synthetase (gamma-GCS) mRNA, protein, and enzymatic specific activity were measured in kidney tissue after BDL. After BDL, kidney GSH and GSSG increased within hours by 67 and 66%, respectively. The increases were not related to plasma glutathione, which decreased below control values. Intravenous bile acid loading caused identical increases in GSH and GSSG as occurred after BDL, when glycine- or taurine-conjugated dihydroxy bile acids were administered. Glutathione consumption, as estimated after blocking of de novo synthesis with BSO, was significantly increased after BDL (127 vs. 44 nmol x g-1 x min-1). gamma-GCS mRNA and enzymatic specific activity were significantly reduced 5 days after BDL, whereas protein concentrations did not change. The urinary sodium concentration was 70% lower in BDL than in control rats. Depletion of renal glutathione normalized sodium excretion by increasing urinary sodium concentration and urinary volume. The increase in kidney glutathione after BDL seems to be mediated by an increase in plasma bile acids and is critically related to sodium retention. The increase in GSH consumption despite reduced gamma-GCS activity indicates a decreased GSH turnover tentatively due to reduced renal GSH efflux by competition with organic anions at membrane transport proteins.

Ca2+- and PKC-dependent stimulation of PGE2 synthesis by deoxycholic acid in human colonic fibroblasts

We investigated prostanoid biogenesis by human colonic fibroblasts (CCD-18Co cells and nine primary fibroblast cultures) exposed to a primary (cholic, CA) or a secondary (deoxycholic, DCA) bile acid. Basal PGE2 levels in CCD-18Co cultures and fibroblast strains initiated from normal and adenocarcinomatous colon, respectively, were 1.7 +/- 0.3, 4.0 +/- 2.0, and 15.0 +/- 4.8 ng/mg protein. Peak levels 24 h after exposure to DCA (300 microM) rose, respectively, seven-, six- and sevenfold, but CA elicited no such responses. Increases in PGE2 synthesis were preceded by sequential increases in PGH synthase-2 mRNA and protein expression and were fully prevented by a nonselective (indomethacin) or a selective (celecoxib) nonsteroidal anti-inflammatory drug. DCA, but not CA, caused abrupt, transient increases in fibroblast intracellular Ca2+ concentration ([Ca2+]i) approximately 1 min after exposure. Increased [Ca2+]i was required for DCA-mediated induction of PGE2 synthesis, and protein kinase C was a further essential component of this signaling pathway. Colonic fibroblasts may be a major target for prostanoid biogenesis induced by fecal bile acids and, potentially, other noxious actions of these agents.

Nitric oxide ameliorates hydrophobic bile acid-induced apoptosis in isolated rat hepatocytes by non-mitochondrial pathways

Hydrophobic bile acids are toxic to isolated rat hepatocytes by mechanisms involving mitochondrial dysfunction and oxidative stress. In the current study we examined the role of nitric oxide (NO), a potential mediator of apoptosis, during bile acid-induced apoptosis. Freshly isolated rat hepatocytes and hepatic mitochondria generated NO and peroxynitrite (ONOO(-)) in a concentration- and time-dependent manner when exposed to the toxic bile salt glycochenodeoxycholate (GCDC) (25-500 microm), which was prevented by the nitric-oxide synthase (NOS) inhibitors N(G)-monomethyl-N-arginine monoacetate (l-NMMA) and 1400W. Relationships between hepatocyte NO production and apoptosis were examined by comparing the effects of NOS inhibitors with other inhibitors of GCDC-induced apoptosis. Inhibitors of caspases 8 and 9, the mitochondrial permeability transition blocker cyclosporin A, and the antioxidant idebenone reduced NO generation and apoptosis in GCDC-treated hepatocytes. In contrast, NOS inhibitors had no effect on GCDC-induced apoptosis despite marked reduction of NO and ONOO(-). However, treatment with the NO donors S-nitroso-N-acetylpenicillamine and spermine NONOate [N-(-aminoethyl)N-(2-hydroxy-2-nitrohydrazino)-1,2-ethylenediamine) inhibited apoptosis and caspase 3 activity while significantly elevating NO levels above GCDC-stimulated levels. Neither NO donors nor NOS inhibitors affected GCDC-induced mitochondrial permeability transition or cytochrome c release from liver mitochondria or GCDC-induced mitochondrial depolarization from isolated hepatocytes, suggesting that NO inhibits bile acid-induced hepatocyte apoptosis by a non-mitochondrial-dependent pathway. In conclusion, whereas NO produced from GCDC-treated hepatocytes neither mediates nor protects against bile acid-induced apoptosis, higher levels of NO inhibit GCDC-induced hepatocyte apoptosis by caspase-dependent pathways.

Mesenteric vascular bed responsiveness in bile duct-ligated rats: roles of opioid and nitric oxide systems

Changes in vascular responsiveness are proposed as the basis for some of the cardiovascular complications in cholestasis. Cholestasis is also associated with accumulation of endogenous opioid peptides and evidence of overproduction of nitric oxide (NO). The possible role of NO or opioid system in cholestasis-induced mesenteric vascular bed responsiveness was investigated. Bile duct-ligated and sham-operated rats were treated for 6 days with either normal saline, naltrexone, an opioid antagonist (20 mg/kg/day) or L-NAME (N(omega)-nitro-L-arginine methyl ester), a nitric oxide synthase inhibitor (3 mg/kg/day). After 7 days, the superior mesenteric artery was cannulated and the mesenteric vascular bed was perfused according to the McGregor method. Baseline perfusion pressure of the mesenteric vascular bed was decreased in bile duct-ligated compared to sham-operated animals. ED(50) of phenylephrine-induced vasoconstriction was increased, but vasoconstriction R(max) was not different in the vascular bed of bile duct-ligated rats and of sham-operated ones. Acetylcholine-induced vasorelaxation was impaired in bile duct-ligated rats (increased ED(50) and decreased vasorelaxation R(max)). Sodium nitroprusside-induced vasorelaxation was not different between bile duct-ligated and sham-operated rats, implying that the smooth muscle components of vasorelaxation were intact. Chronic treatment with L-NAME partially restored both the acetylcholine-induced vasorelaxation and phenylephrine-induced vasoconstriction response in bile duct-ligated rats. Naltrexone treatment also partially restored the acetylcholine-induced vasorelaxation and phenylephrine-induced vasoconstriction in bile duct-ligated rats. There is impaired acetylcholine-induced vasorelaxation in cholestatic rats, probably due to a defect in endothelial function. This study also provided evidence for the involvement of increased opioidergic tone and NO overproduction in cholestasis-induced vascular hyporesponsiveness.