Integration of Metabolomics, Lipidomics, and Proteomics Reveals the Metabolic Characterization of Nonalcoholic Steatohepatitis.

Metabolic dysfunction is associated with nonalcoholic steatohepatitis (NASH) development. However, omics studies investigating metabolic changes in NASH patients are limited. In this study, metabolomics and lipidomics in plasma, as well as proteomics in the liver, were performed to characterize the metabolic profiles of NASH patients. Moreover, the accumulation of bile acids (BAs) in NASH patients prompted us to investigate the protective effect of cholestyramine on NASH. The liver expression of essential proteins involved in FA transport and lipid droplets was significantly elevated in patients with NASH. Furthermore, we observed a distinct lipidomic remodeling in patients with NASH. We also report a novel finding suggesting an increase in the expression of critical proteins responsible for glycolysis and the level of glycolytic output (pyruvic acid) in patients with NASH. Furthermore, the accumulation of branched chain amino acids, aromatic amino acids, purines, and BAs was observed in NASH patients. Similarly, a dramatic metabolic disorder was also observed in a NASH mouse model. Cholestyramine not only significantly alleviated liver steatosis and fibrosis but also reversed NASH-induced accumulation of BAs and steroid hormones. In conclusion, NASH patients were characterized by perturbations in FA uptake, lipid droplet formation, glycolysis, and accumulation of BAs and other metabolites.

Effects of Bile Acid Modulation by Dietary Fat, Cholecystectomy, and Bile Acid Sequestrant on Energy, Glucose, and Lipid Metabolism and Gut Microbiota in Mice.

Bile acid metabolism, involved with the digestion and absorption of nutrients in the gut, is linked to the gut microbiota community, greatly impacting the host's metabolism. We examined the hypothesis that the modulation of bile acid metabolism by dietary fat contents, gallbladder removal (GBX; cholecystectomy), and bile acid sequestrant (BAS; cholestyramine) treatment could alter energy, glucose, and lipid metabolism through the changes in the gut microbiota. Mice were randomly assigned to the following six groups: (1) Sham GBX surgery (Sham) + low fat/high carbohydrate diet (LFD), (2) Sham + high fat diet (HFD), (3) Sham + HFD + BAS, (4) GBX + LFD, (5) GBX + HFD, and (6) GBX + HFD + BAS. BAS groups received 2% cholestyramine. After an 8-week intervention, energy, glucose, and lipid metabolism, and the gut microbiota community were measured. HFD groups exhibited higher body weight gain than LFD, and GBX increased the weight gain comped to Sham groups regardless of BAS in HFD (p < 0.05). Homeostatic model assessment for insulin resistance (HOMA-IR) was higher in HFD than LFD, and GBX increased it regardless of BAS. Serum lipid profiles were worsened in GBX + HFD compared to Sham + LFD, whereas BAS alleviated them, except for serum HDL cholesterol. Hepatic tumor-necrosis-factor-α (TNF-α) mRNA expression and lipid peroxide contents increased with GBX and BAS treatment compared to Sham and no BAS treatment (p < 0.05). Hepatic mRNA expression of sterol regulatory element-binding transcription factor 1c (SREBP1c) and peroxisome proliferator-activated receptor gamma (PPAR-γ) exhibited the same trend as that of tumor necrosis factor-α (TNF-α). The α-diversity of gut bacteria decreased in GBX + HFD and increased in GBX + HFD + BAS. Akkermentia, Dehalobacterium, SMB53, and Megamonas were high in the Sham + LFD, and Veillonella and Streptococcus were rich in the Sham + HFD, while Oscillospira and Olsenella were high in Sham + HFD + BAS (p < 0.05). GBX + LFD increased Lactobacillus and Sutterella while GBX + HFD + BAS elevated Clostridium, Alistipes, Blautia, Eubacterium, and Coprobacillus (p < 0.05). In conclusion, the modulation of bile acid metabolism influences energy, glucose, and lipid metabolisms, and it might be linked to changes in the gut microbiota by bile acid metabolism modulation.

Preparation of nanoliposomes by microfluidic mixing in herring-bone channel and the role of membrane fluidity in liposomes formation.

Introduction of microfluidic mixing technique opens a new door for preparation of the liposomes and lipid-based nanoparticles by on-chip technologies that are applicable in a laboratory and industrial scale. This study demonstrates the role of phospholipid bilayer fragment as the key intermediate in the mechanism of liposome formation by microfluidic mixing in the channel with "herring-bone" geometry used with the instrument NanoAssemblr. The fluidity of the lipid bilayer expressed as fluorescence anisotropy of the probe N,N,N-Trimethyl-4-(6-phenyl-1,3,5-hexatrien-1-yl) was found to be the basic parameter affecting the final size of formed liposomes prepared by microfluidic mixing of an ethanol solution of lipids and water phase. Both saturated and unsaturated lipids together with various content of cholesterol were used for liposome preparation and it was demonstrated, that an increase in fluidity results in a decrease of liposome size as analyzed by DLS. Gadolinium chelating lipids were used to visualize the fine structure of liposomes and bilayer fragments by CryoTEM. Experimental data and theoretical calculations are in good accordance with the theory of lipid disc micelle vesiculation.

Membrane cholesterol depletion reduces downstream signaling activity of the adenosine A2A receptor.

Cholesterol has been shown to modulate the activity of multiple G Protein-coupled receptors (GPCRs), yet whether cholesterol acts through specific interactions, indirectly via modifications to the membrane, or via both mechanisms is not well understood. High-resolution crystal structures of GPCRs have identified bound cholesterols; based on a ß2-adrenergic receptor (ß2AR) structure bound to cholesterol and the presence of conserved amino acids in class A receptors, the cholesterol consensus motif (CCM) was identified. Here in mammalian cells expressing the adenosine A2A receptor (A2AR), ligand dependent production of cAMP is reduced following membrane cholesterol depletion with methyl-beta-cyclodextrin (MßCD), indicating that A2AR signaling is dependent on cholesterol. In contrast, ligand binding is not dependent on cholesterol depletion. All-atom molecular simulations suggest that cholesterol interacts specifically with the CCM when the receptor is in an active state, but not when in an inactive state. Taken together, the data support a model of receptor state-dependent binding between cholesterol and the CCM, which could facilitate both G-protein coupling and downstream signaling of A2AR.

Cholestyramine as a promising, strong anion exchange resin for direct capture of genetic biomarkers from raw pancreatic fluids.

The ability to capture cell-free DNA from the gastrointestinal tract, in a minimally invasive manner, could enhance our ability to diagnose gastrointestinal disease, or gain a better understanding of the spatial mapping of the intestinal microbiota. We, therefore, sought to identify a class of capture agents that could directly and efficiently sequester genetic material from intestinal fluids. As a particular case study, we examined the ability to capture DNA from pancreatic secretions, for potential application in enabling the sequestration of early, genetic biomarkers of pancreatic disease. We hypothesized that the cholestyramine series of strong cation exchange resins, which are FDA approved for the treatment of high cholesterol, may be capable of capturing DNA from pancreatic secretions. We identified a particular cholestyramine resin, DOWEX 1 × 2 100-200 mesh, which is able to efficiently capture and purify DNA from pancreatic fluid. Using only 200 µL of pancreatic secretions, we are able to recover 247 ± 182 ng of amplifiable human DNA, giving an estimated pancreatic fluid DNA content of 1.23 ± 0.91 ng/µL. To our knowledge, this is the first demonstration of a material that can effectively capture and purify DNA directly from untreated pancreatic fluids. Thus, our approach could hold high utility for the in vivo capture of DNA and disease biomarkers if incorporated into an appropriate sampling device. Biotechnol. Bioeng. 2017;114: 934-938. © 2016 Wiley Periodicals, Inc.

Grape Seed Procyanidins and Cholestyramine Differentially Alter Bile Acid and Cholesterol Homeostatic Gene Expression in Mouse Intestine and Liver.

Bile acid (BA) sequestrants, lipid-lowering agents, may be prescribed as a monotherapy or combination therapy to reduce the risk of coronary artery disease. Over 33% of adults in the United States use complementary and alternative medicine strategies, and we recently reported that grape seed procyanidin extract (GSPE) reduces enterohepatic BA recirculation as a means to reduce serum triglyceride (TG) levels. The current study was therefore designed to assess the effects on BA, cholesterol and TG homeostatic gene expression following co-administration with GSPE and the BA sequestrant, cholestyramine (CHY). Eight-week old male C57BL/6 mice were treated for 4 weeks with either a control or 2% CHY-supplemented diet, after which, they were administered vehicle or GSPE for 14 hours. Liver and intestines were harvested and gene expression was analyzed. BA, cholesterol, non-esterified fatty acid and TG levels were also analyzed in serum and feces. Results reveal that GSPE treatment alone, and co-administration with CHY, regulates BA, cholesterol and TG metabolism differently than CHY administration alone. Notably, GSPE decreased intestinal apical sodium-dependent bile acid transporter (Asbt) gene expression, while CHY significantly induced expression. Administration with GSPE or CHY robustly induced hepatic BA biosynthetic gene expression, especially cholesterol 7α-hydroxylase (Cyp7a1), compared to control, while co-administration further enhanced expression. Treatment with CHY induced both intestinal and hepatic cholesterologenic gene expression, while co-administration with GSPE attenuated the CHY-induced increase in the liver but not intestine. CHY also induced hepatic lipogenic gene expression, which was attenuated by co-administration with GSPE. Consequently, a 25% decrease in serum TG levels was observed in the CHY+GSPE group, compared to the CHY group. Collectively, this study presents novel evidence demonstrating that GSPE provides additive and complementary efficacy as a lipid-lowering combination therapy in conjunction with CHY by attenuating hepatic cholesterol synthesis, enhancing BA biosynthesis and decreasing lipogenesis, which warrants further investigation.

Effect of Bile Acid Sequestrants on the Risk of Cardiovascular Events: A Mendelian Randomization Analysis.

BACKGROUND: Statins lower low-density lipoprotein cholesterol (LDL-C) and risk of coronary artery disease (CAD), but they may be ineffective or not tolerated. Bile acid sequestrants (BAS) reduce LDL-C, yet their clinical efficacy on CAD remains controversial. METHODS AND RESULTS: We conducted a systematic review and meta-analysis of randomized controlled trials to assess the effect of cholestyramine and colesevelam. We then used Mendelian randomization to estimate the effect of BAS on reducing the risk of CAD. First, we quantified the effect of rs4299376 (ABCG5/ABCG8), which affects the intestinal cholesterol absorption pathway targeted by BAS and then we used these estimates to predict the effect of BAS on CAD. Nineteen randomized controlled trials with a total of 7021 study participants were included. Cholestyramine 24 g/d was associated with a reduction in LDL-C of 23.5 mg/dL (95% confidence interval [CI] -26.8,-20.2; N=3806) and a trend toward reduced risk of CAD (odds ratio 0.81, 95% CI 0.70-1.02; P=0.07; N=3806), whereas colesevelam 3.75 g/d was associated with a reduction in LDL-C of 22.7 mg/dL (95% CI -28.3, -17.2; N=759). Based on the findings that rs4299376 was associated with a 2.75 mg/dL decrease in LDL-C and a 5% decrease in risk of CAD outcomes, we estimated that cholestyramine was associated with an odds ratio for CAD of 0.63 (95% CI 0.52-0.77; P=6.3×10(-6)) and colesevelam with an odds ratio of 0.64 (95% CI 0.52-0.79, P=4.3×10(-5)), which were not statistically different from BAS clinical trials (P>0.05). CONCLUSIONS: The cholesterol lowering effect of BAS may translate into a clinically relevant reduction in CAD.

The potential use of cholestyramine to reduce the risk of developing Clostridium difficile-associated diarrhoea in patients receiving long-term intravenous ceftriaxone.

Intravenous pharmacotherapy with the third-generation cephalosporin ceftriaxone is unfortunately associated with a relatively high incidence of Clostridium difficile-associated diarrhoea. Cholestyramine (colestyramine) is an anion-binding resin which can bind luminal C.difficile toxin A (TcdA) and toxin B (TcdB) and which may be beneficial in the treatment of recurrent antibiotic-associated pseudomembranous colitis. We therefore hypothesised that concomitant oral cholestyramine might reduce the risk of C.difficile-associated diarrhoea in patients receiving long-term intravenous ceftriaxone. A pilot study was carried out in which it was found that only three out of 46 (6.5%) such patients being treated with 2 g ceftriaxone daily for Lyme borreliosis, who also received 4 g cholestyramine daily, developed C.difficile-associated diarrhoea. This is smaller than a published report of the incidence of this complication in six out of 26 (23.1%) patients following 1-3 days' treatment with 1 g intravenous ceftriaxone, but without oral cholestyramine (p=0.06). We therefore recommend that a larger, double-blind placebo-controlled trial be carried out to test this hypothesis.

Active transport of bile acids decreases mucin 2 in neonatal ileum: implications for development of necrotizing enterocolitis.

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency of premature infants, but its etiology remains unclear. We have previously shown that mucin 2 (Muc2) positive goblet cells are significantly decreased in NEC. We have also shown that ileal bile acids (BAs) are significantly increased during the development of this disease. Because BAs can affect mucins, we hypothesized that elevated ileal BAs contribute to decreased Muc2 in experimental NEC. The role of Muc2 in NEC was evaluated in Winnie +/+ mice, a strain that produces aberrant Muc2. Muc2 and trefoil factor 3 (Tff3) were assessed in neonatal rats subjected to the NEC protocol when bile acids were removed, and in ileal explants from newborn and older rats cultured with and without BAs. Further, the role of active transport of BAs was determined using neonatal rats given the apical sodium dependent bile acid transporter (Asbt) inhibitor SC-435 and in neonatal Asbt knockout mice subjected to the NEC protocol. Mice with aberrant Muc2 had significantly greater incidence and severity of NEC. Using both in vivo and ex vivo techniques, we determined that BAs decrease Muc2 positive cells in neonatal but not older ileum. However, Tff3 positive cells are not decreased by BAs. In addition, active transport of BAs is required for BAs to decrease Muc2 in immature ileum. These data show that functional Muc2 plays a critical role in the prevention of NEC and BAs can potentiate the decreased Muc2 in disease development. Further, BAs have a more profound effect on Muc2 in immature versus older ileum, which may explain at least in part why NEC occurs almost exclusively in premature infants.

Degradation of 24S-hydroxycholesterol in men is not regulated by CYP7A1.

OBJECTIVE: The conversion of cholesterol into bile acids occurs via a long cascade of enzymatically regulated oxidative processes. Our aim was to examine if an up-regulation of hepatic cholesterol 7alpha-hydroxylase (CYP7A1) in humans by cholestyramine, a bile acid-binding resin, has an effect on the degradation of brain-specific 24S-hydroxycholesterol. PATIENTS AND METHODS: Six normocholesterolemic male volunteers received 4 g cholestyramine b.i.d. for 2 weeks in an open, prospective exploratory trial. Serum concentrations of lipoproteins and triglycerides were measured by routine enzymatic assays. Sterols and oxysterols were measured by gas chromatography/mass spectrometry. RESULTS: Total and LDL-cholesterol decreased on the average by 9.3% (p = 0.002) and 19.8% (p = 0.001) after 2 weeks of treatment, respectively. Absolute serum concentrations of 7alpha-hydroxycholesterol, a marker for bile acid production, increased 4-fold after 2 weeks, while 24S- and 27-hydroxycholesterol remained unchanged. Treatment with cholestyramine elevated serum levels of lathosterol, an indicator for the endogenous synthesis of cholesterol, by 146% (p = 0.009). CONCLUSION: In addition to lowering serum concentrations of total cholesterol and LDL-cholesterol, cholestyramine at a dose rate of 4 g b.i.d. causes a significant increase in the CYP7A1 catalyzed 7alpha-hydroxylation of cholesterol and an up-regulation of endogenous cholesterol synthesis, as proven indirectly by an increase in serum lathosterol levels. Total serum levels of 24S- and 27-hydroxycholesterol remained unchanged indicating that an up-regulation in CYP7A1 activity is not responsible for the subsequent oxidative degradation of these hydroxylated sterols.

Enhancement of dietary protein digestion by conjugated bile acids.

BACKGROUND & AIMS: Conjugated bile acids promote absorption of dietary lipids by solubilizing them in mixed micelles. Bile acids are not considered to facilitate the digestion of other nutrients. METHODS: The effect of conjugated bile acids on the rate of protein hydrolysis by trypsin and chymotrypsin was examined in vitro. Common dietary proteins and 2 bacterial glutenases (proposed oral therapies for celiac sprue) were proteolyzed in the absence or presence of a 10 mmol/L conjugated bile acid mixture, simulating human bile composition. Lipolysis products (monoolein) and fatty acid were also evaluated to simulate postprandial intestinal contents. RESULTS: Conjugated bile acids dramatically enhanced the proteolysis of several dietary proteins, including beta-lactoglobulin, bovine serum albumin, myoglobin, and a commercially available dietary protein supplement. For beta-lactoglobulin, a cow's milk allergen that is resistant to pepsin cleavage, bile acids enhanced its proteolysis by pancreatic proteases even after incubation under gastric conditions. Exposure of prolyl endopeptidases to bile acids made them more susceptible to pancreatic proteases under simulated intestinal conditions. The conjugated bile acid effect was most pronounced in the presence of dihydroxy bile acids and was observable at bile concentrations below the critical micellar concentration but to a much greater extent at concentrations above the critical micellar concentration. CONCLUSIONS: We propose that, in addition to promoting lipid absorption, conjugated bile acids affect the digestion and assimilation of dietary proteins by accelerating hydrolysis by pancreatic proteases. These findings have implications for intraluminal protein breakdown and assimilation in the upper small intestine.

Niemann-Pick C1 expression is not regulated by the amount of cholesterol flowing through cells in the mouse.

The Niemann-Pick C1 (NPC1) protein functions to regulate the transport of cholesterol from late endosomes/lysosomes to other cellular compartments after lipoprotein uptake through the coated-pit pathway. The present study examines the relative expression of NPC1 mRNA and NPC1 protein in different tissues of the mouse in relation to the uptake of total cholesterol carried in chylomicron remnants (CMr-TC), low density lipoproteins (LDL-TC), cholesteryl ester carried in high density lipoproteins (HDL-CE), and cholesterol synthesis. Results from this study demonstrate that the highest relative expression of NPC1 is in the liver, which is also the tissue with the highest uptake of CMr-TC, LDL-TC, HDL-CE, and cholesterol synthesis. However, there was no similar relation in the remaining tissues. To examine the relative expression of NPC1 in relation to the amount of cholesterol that flowed through the coated-pit pathway, mice were fed a diet supplemented with increasing amounts of cholesterol or cholestyramine. The results from this study demonstrated that there was no relation between the relative expression of NPC1 and the amount of cholesterol that flowed through the coated-pit pathway. We conclude that the relative expression of NPC1 is not regulated by the flow of cholesterol through cells in the mouse and is therefore constitutive.

Reduction in fecal excretion of Giardia cysts: effect of cholestasis and diet.

Bile is a major growth factor for the proliferation of Giardia spp. trophozoites in the small intestine and, at high concentrations, stimulates encystment of trophozoites. This report demonstrates that surgical cholestasis to interrupt the flow of bile from liver to intestine or the use of bile-binding resins in the diet can both dramatically decrease the fecal excretion of Giardia muris cysts. Cholestasis produced a 3 log reduction in excretion of G. muris cysts within 24 hr of surgery and a 4 log reduction after 3 days. Sham controls showed no difference in cyst excretion from presurgical control values. Two isocaloric diets were studied: a control diet (N) of Purina mouse chow containing 5% celufil and an experimental diet (CR) containing 5% cholestyramine, a resin that binds bile. Compared with the N diet, the CR diet was associated with reductions in cyst excretion of 3 logs within 1 day. Despite lowered excretion of G. muris cysts in mice fed the cholestyramine diet, the trophozoite recovery from the duodenum was similar with both diets. Cyclic feeding of the CR diet and the N diet at 3-day intervals produced significant oscillations (changes of 3-4 logs) in fecal cyst shedding. The significant reductions in fecal excretion of cysts observed with agents that bind bile suggests that diets capable of binding bile might be a therapeutic means to minimize the fecal excretion of cysts and thereby may help to reduce the risk of spreading giardiasis through fecal-oral contamination.

In vitro studies on the evaluation of mycotoxin detoxifying agents for their efficacy on deoxynivalenol and zearalenone.

A simple in vitro system was developed to study the efficacy of commercially available mycotoxin detoxifying agents and adsorbing substances as feed additives to detoxify deoxynivalenol (DON) and zearalenone (ZON) in situ. The in vitro model simulates the conditions (pH, temperature and transit time) of the porcine gastrointestinal tract, as pigs react most sensitively to these mycotoxins. The commercially available products were not effective in detoxifying DON and ZON under the applied conditions, while activated carbon was able to bind both toxins and cholestyramine, and a modified aluminosilicate showed good adsorption abilities for ZON. Data obtained in dose dependency studies showed an estimated adsorption capacity of cholestyramine and the modified aluminosilicate of 11.7 and 5.7 g ZON/kg detoxifying agent. The in vitro system deployed in the present study was demonstrated to be a simple, helpful tool in screening substances for their ability to detoxify DON and ZON under the simulated conditions of the porcine gastrointestinal tract. Nonetheless in vivo experiments are indispensable to proof the efficacy.

Differential expression of cholangiocyte and ileal bile acid transporters following bile acid supplementation and depletion.

AIM: We have previously demonstrated that cholangiocytes, the epithelial cells lining intrahepatic bile ducts, encode two functional bile acid transporters via alternative splicing of a single gene to facilitate bile acid vectorial transport. Cholangiocytes possess ASBT, an apical sodium-dependent bile acid transporter to take up bile acids, and t-ASBT, a basolateral alternatively spliced and truncated form of ASBT to efflux bile acids. Though hepatocyte and ileal bile acid transporters are in part regulated by the flux of bile acids, the effect of alterations in bile acid flux on the expression of t-ASBT in terminal ileocytes remains unclear. Thus, we tested the hypothesis that expression of ASBT and t-ASBT in cholangiocytes and ileocytes was regulated by bile acid flux. METHODS: Expression of ASBT and t-ASBT message and protein in cholangiocytes and ileocytes isolated from pair-fed rats given control (C) and 1% taurocholate (TCA) or 5% cholestyramine (CY) enriched diets, were assessed by both quantitative RNase protection assays and quantitative immunoblotting. The data obtained from each of the control groups were pooled to reflect the changes observed following TCA and CY treatments with respect to the control diets. Cholangiocyte taurocholate uptake was determined using a novel microperfusion technique on intrahepatic bile duct units (IBDUs) derived from C, TCA and CY fed rats. RESULTS: In cholangiocytes, both ASBT and t-ASBT message RNA and protein were significantly decreased in response to TCA feeding compared to C diet. In contrast, message and protein of both bile acid transporters significantly increased following CY feeding compared to C diet. In the ileum, TCA feeding significantly up-regulated both ASBT and t-ASBT message and protein compared to C diet, while CY feeding significantly down-regulated message and protein of both bile acid transporters compared to C diet. As anticipated from alterations in cholangiocyte ASBT expression, the uptake of taurocholate in microperfused IBDUs derived from rats on TCA diet decreased 2.7-fold, whereas it increased 1.7-fold in those on CY diet compared to C diet fed groups. CONCLUSION: These data demonstrate that expression of ASBT and t-ASBT in cholangiocytes is regulated by a negative feedback loop while the expression of these transporters in terminal ileum is modified via positive feedback. Thus, while transcriptional regulatory mechanisms in response to alterations in bile acid pool size are operative in both cholangiocytes and ileocytes, each cell type responds differently to bile acid supplementation and depletion.

Regulation of hepatic low-density lipoprotein receptor, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and cholesterol 7alpha-hydroxylase mRNAs in human liver.

To characterize the coordinate regulation of cholesterol metabolism in human liver, we simultaneously quantified mRNA levels of cholesterol 7alpha-hydroxylase (CYP7A1), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), and low- density lipoprotein receptors (LDLRs) in liver biopsies from 76 patients undergoing cholecystectomy. The three transcript levels were not different between untreated gallstone and gallstone-free patients and not significantly altered by 10-d exclusion of dietary cholesterol. Treatment with chenodeoxycholic acid suppressed CYP7A1 and to a lesser extent HMGR mRNA levels. Cholestyramine treatment increased CYP7A1, but also HMGR and LDLR mRNA, and statins only increased HMGR mRNA. Resin + statin treatment increased all mRNA species. In untreated patients, the mRNA levels of HMGR and LDLR were more strongly correlated (r = +0.60) than those of CYP7A1 and HMGR (r = +0.49) or CYP7A1 and LDLR (r = +0.21). In the treated patients, in whom bile acid synthesis was suppressed or stimulated, mRNA levels of CYP7A1 and HMGR (r = +0.84) as well as CYP7A1 and LDLR (r = +0.62) were more strongly correlated than those of HMGR and LDLR (r = +0.59). The coordinate control of HMGR and LDLR mRNA levels reflects their common regulation by shared transcriptional activation. In contrast, following changes in bile acid flux through the liver, CYP7A1 gene expression becomes a strong modulator of hepatic cholesterol metabolism.

New therapies on the horizon.

Statins have proved to be potent drugs for reducing low-density lipoprotein cholesterol (LDL-C) levels. However, because the response to current statin therapy regimens is not always sufficient to reach defined goal levels, additional drugs to lower LDL-C are needed. New drugs may soon be available to lower LDL-C levels by mechanisms that differ from those of the statins. Among these new agents are a bile acid binding resin, inhibitors of bile acid transport, inhibitors of cholesterol transport, inhibitors of cholesterol esterification, and triglyceride-lowering agents.

Bile acid sequestrants based on cationic dextran hydrogel microspheres. 2. Influence of the length of alkyl substituents at the amino groups of the sorbents on the sorption of bile salts.

Cationic dextran hydrogel microspheres with pendant quaternary ammonium groups having alkyl substituents (C(2)-C(12)) at quaternary nitrogen were synthesized. The in vitro sorption of sodium salts of four bile acids (glycocholic, cholic, taurocholic, and deoxycholic acids) with these hydrogels was studied as a function of substituent alkyl chain length and bile acid hydrophobicity. Sorption experiments were performed in phosphate buffer solutions (pH 7.4) containing one bile salt (individual sorption) or mixtures of several bile salts (competitive sorption). Parameters for individual sorption were calculated taking into consideration the stoichiometric and cooperative binding of bile salts to oppositely charged polymer hydrogels. The results show that the increase in the length of the alkyl chain of the substituent leads to an increase in both ionization constant K(0) and overall stability constant of binding K, but decreases the cooperativity parameter u. The competitive sorption studies indicate that the hydrogels display a good affinity for both dihydroxylic and trihydroxylic bile salts. The molar ratio of maximum amounts bound for the two types of bile acid is 2 to 1, which is much lower than those reported for other cationic polymers recommended as bile acid sequestrants. The binding constants for the sorption of bile salts by some dextran hydrogels are 20-30 times higher than those obtained for cholestyramine under similar sorption conditions.

Acute intraduodenal bile salt depletion leads to strong gallbladder contraction, altered antroduodenal motility and high plasma motilin levels in humans.

Cholecystokinin is the main hormone involved in postprandial gallbladder contraction. There is also considerable gallbladder contraction in the fasting state, associated with phase III of the gastrointestinal migrating motor complex and release of the hormone motilin. It has been proposed that intraduodenal bile salts exert a negative-feedback control on postprandial cholecystokinin release and resulting gallbladder contraction. We wanted to elucidate whether a similar control mechanism on gallbladder contraction exists in the fasting state. We therefore performed gallbladder ultrasonography and 24-h antroduodenal motility registrations and determined plasma cholecystokinin and motilin levels in six healthy subjects before and after acute (4 g) and chronic (8 days; 8 g day(-1)) oral cholestyramine. Acute cholestyramine strongly decreased gallbladder volumes and increased motilin without changed cholecystokinin levels. There was a negative relationship between gallbladder volumes and plasma motilin levels. Although there was a persistent fasting pattern of antroduodenal motility, its cycle length was increased (P < 0.03) with markedly longer phase II (P < 0. 005). Fasting gallbladder volumes 24 h later were still strongly decreased but gradually increased to pretreatment levels. Before and after 8 days cholestyramine, interdigestive and postprandial gallbladder emptying, intestinal migrating motor complex and hormone levels did not differ. We conclude that acute (but not chronic) intraduodenal bile salt depletion with cholestyramine affects gallbladder and antroduodenal motility, possibly partly related to motilin release.