Molecular interactions between bile salts, phospholipids and cholesterol : relevance to bile formation, cholesterol crystallization and bile salt toxicity

Cholesterol is a nonpolar lipid dietary constituent, absorbed from the small intestine, transported in blood and taken up by the liver. In bile, the sterol is solubilized in mixed micelles by bile salts and phospholipids. In case of supersaturation, cholesterol is kept in vesicles with phospholipid or phase-separated as crystals. Accurate isolation of micellar and vesicular lipid carriers in model systems is important for the study of the cholesterol crystallization and gallstone formation. A new method for separating lipid carriers in model biles has been proposed in this thesis. Also, the key role of bile salts and phospholipids in cholesterol solubilization in bile is described, together with their modulating/protecting effects on cholesterol supersaturation and crystallization. Apart from cholesterol crystallization, this thesis also focused on the process of nascent bile formation at the level of the hepatocyte canalicular membrane. Phosphatidylcholine is the predominant phospholipid in bile, although both sphingomyelin and phosphatidylcholine are the major structural phospholipids in the outer leaflet of the hepatocyte canalicular membrane. Different physical-chemical characteristics of the two phospholipids may relate to their different distribution in vivo. We have studied by means of spectrophotometry and by sequential state-of-the-art cryo-transmission electron microscopy, effects of including sphingomyelin within phosphatylcholine-containing vesicles (with and without cholesterol) on vesicle ? micelle phase transitions that were induced by addition of bile salts. Cholesterol plays a key role in formation of pathophysiologically relevant phosphatidylcholine plus sphingomyelin-containing bilayers and in modulating interactions between vesicles and detergent bile salts. The entero-hepatic circulation and the detergent activity of the bile salts are discussed int he last part of the thesis. Bile salts may present as good or bad guys. The good aspect is their effect in intestinal lipid absorption, bile formation and cholesterol solubilization. The bad aspect is the potential cytotoxicity induced by the detergent bile salts. The presence of phospholipids within bile salt micelles protects against bile salt-induced cytotoxicity. When compared to egg yolk phosphatidylcholine, sphingomyelin offered greatly enhanced protection against bile salt-induced cytotoxicity compared to egg yolk phosphatidylcholine. Last, epidemiological and experimental studies have indicated a consistent correlation between increased risk of colon cancer and elevated levels of fecal bile salts in Western populations that consume high-fat diets. Deoxycholate, a secondary bile salts present in the colon, may act as a tumor promoter, inducing hyperproliferation and increasing the number of tumors elicited by complete carcinogens. Appreciable amounts of dietary sphingomyelin appear to reach to the colon. In CaCo-2 cells, we have shown that pathophysiologically relevant concentrations of this bile salt induced dose-dependent apoptosis in the early stages of incubation, but hyperproliferation at later stages. Sphingomyelin dose-dependently inhibited apoptosis as well as hyperproliferation, presumably through a local effect on deoxycholate activity. These findings may have important implications for colon cancer prevention

FXR agonists and FGF15 reduce fecal bile acid excretion in a mouse model of bile acid malabsorption

Bile acid malabsorption, which in patients leads to excessive fecal bile acid excretion and diarrhea, is characterized by a vicious cycle in which the feedback regulation of bile acid synthesis is interrupted, resulting in additional bile acid production. Feedback regulation of bile acid synthesis is under the control of an endocrine pathway wherein activation of the nuclear bile acid receptor, farnesoid X receptor (FXR), induces enteric expression of the hormone, fibroblast growth factor 15 (FGF15). In liver, FGF15 acts together with FXR-mediated expression of small heterodimer partner to repress bile acid synthesis. Here, we show that the FXR-FGF15 pathway is disrupted in mice lacking apical ileal bile acid transporter, a model of bile acid malabsorption. Treatment of Asbt-/- mice with either a synthetic FXR agonist or FGF15 downregulates hepatic cholesterol 7alpha-hydroxylase mRNA levels, decreases bile acid pool size, and reduces fecal bile acid excretion. These findings suggest that FXR agonists or FGF15 could be used therapeutically to interrupt the cycle of excessive bile acid production in patients with bile acid malabsorption

Microbiota Modification with Probiotics Induces Hepatic Bile Acid Synthesis via Downregulation of the Fxr-Fgf15 Axis in Mice

Gut microbiota influences host health status by providing trophic, protective, and metabolic functions, including bile acid (BA) biotransformation. Microbial imprinting on BA signature modifies pool size and hydrophobicity, thus contributing to BA enterohepatic circulation. Microbiota-targeted therapies are now emerging as effective strategies for preventing and/or treating gut-related diseases. Here, we show that gut microbiota modulation induced by VSL#3 probiotics enhances BA deconjugation and fecal excretion in mice. These events are associated with changes in ileal BA absorption, repression of the enterohepatic farnesoid X receptor-fibroblast growth factor 15 (FXR-FGF15) axis, and increased hepatic BA neosynthesis. Treatment with a FXR agonist normalized fecal BA levels in probiotic-administered mice, whereas probiotic-induced alterations in BA metabolism are abolished upon FXR and FGF15 deficiency. Our data provide clear in vivo evidence that VSL#3 probiotics promote ileal BA deconjugation with subsequent fecal BA excretion and induce hepatic BA neosynthesis via downregulation of the gut-liver FXR-FGF15 axis

Incorporation of cholesterol in sphingomyelin- phosphatidylcholine vesicles has profound effects on detergent-induced phase transitions

Abstract Vesicle ↔ micelle transitions are important phenomena during bile formation and intestinal lipid processing. The hepatocyte canalicular membrane outer leaflet contains appreciable amounts of phosphatidylcholine (PC) and sphingomyelin (SM), and both phospholipids are found in the human diet. Dietary SM enrichment inhibits intestinal cholesterol absorption. We therefore studied detergent-induced vesicle → micelle transitions in SM-PC vesicles. Phase transitions were evaluated by spectrophotometry and cryotransmission electron microscopy (cryo-TEM) after addition of taurocholate (3–7 mM) to SM-PC vesicles (4 mM phospholipid, SM/PC 40%/60%, without or with 1.6 mM cholesterol). After addition of excess (5–7 mM) taurocholate, SM-PC vesicles were more sensitive to micellization than PC vesicles. As shown by sequential cryo-TEM, addition of equimolar (4 mM) taurocholate to SM-PC vesicles induced formation of open vesicles, then (at the absorbance peak) fusion of bilayer fragments into large open structures (around 200 nm diameter) coexisting with some multilamellar or fused vesicles and thread-like micelles and, finally, transformation into an uniform picture with long thread-like micelles. Incorporation of cholesterol in the SM/PC bilayer changed initial vesicular shape from spherical into ellipsoid and profoundly increased detergent resistance. Disk-like micelles and multilamellar vesicles, and then extremely large vesicular structures, were observed by sequential cryo-TEM under these circumstances, with persistently increased absorbance values by spectrophotometry. These findings may be relevant for bile formation and intestinal lipid processing. Inhibition of intestinal cholesterol absorption by dietary SM enrichment may relate to high resistance against bile salt-induced micellization of intestinal lipids in presence of the sphingolipid

Role of unenhanced breast MRI for detecting and differentiating breast lesions

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Hepatic microRNA Expression by PGC-1α and PGC-1β in the Mouse.

The fine-tuning of liver metabolism is essential to maintain the whole-body homeostasis and to prevent the onset of diseases. The peroxisome proliferator-activated receptor-γ coactivators (PGC-1s) are transcriptional key players of liver metabolism, able to regulate mitochondrial function, gluconeogenesis and lipid metabolism. Their activity is accurately modulated by post-translational modifications. Here, we showed that specific PGC-1s expression can lead to the upregulation of different microRNAs widely implicated in liver physiology and diseases development and progression, thus offering a new layer of complexity in the control of hepatic metabolism

Uremic lung: The “calcified cauliflower” sign in the end stage renal disease

AbstractMetastatic pulmonary calcification (MPC) is a rare pathological condition consisting of lung calcium salt deposits which commonly occurs in patients affected by chronic kidney disease probably for some abnormalities in calcium and phosphate metabolism. CT represents the technique of choice for detecting MPC findings including ground glass opacities and partially calcified nodules or consolidations. We present a case of MCP in a patient affected by hepato-renal autosomic-dominant polycystic disease; chest CT revealed extensive lobar-segmental parenchymal calcification with a peculiar cauliflower shape which we called “calcified cauliflower” sign. The “calcified cauliflower” sign can be reported as a new CT pattern of uremic lung that needs to be identified for a correct diagnosis and patient management

Induction Therapy and Stem Cell Mobilization in Patients with Newly Diagnosed Multiple Myeloma

Autologous stem cell transplantation (ASCT) is considered the standard therapy for younger patients with newly diagnosed symptomatic multiple myeloma (MM). The introduction into clinical practice of novel agents, such as the proteasome inhibitor bortezomib and the immunomodulatory derivatives (IMiDs) thalidomide and lenalidomide, has significantly contributed to major advances in MM therapy and prognosis. These novel agents are incorporated into induction regimens to enhance the depth of response before ASCT and further improve post-ASCT outcomes. Between January 2000 and November 2011, 65 patients with MM were transplanted in the Department of Biomedical Science and Clinical Oncology at the University of Bari. According to Durie-Salmon, 60 patients had stage III of disease and 5 stage II. Only 7 patients were in stage B (renal failure). Induction regimens that were administered in two or more cycles were VAD (vincristine, adriamycin, and dexamethasone), Thal-Dex (thalidomide, dexamethasone), Len-Dex (lenalidomide, dexamethasone), Vel-Dex (bortezomib, dexamethasone), VTD (bortezomib, thalidomide, and dexamethasone), and PAD (bortezomib, pegylated liposomal doxorubicin, and dexamethasone). In mobilization procedure, the patients received cyclophosphamide and granulocyte colony-stimulating factor (G-CSF). The number of cells collected through two or more leukapheresess, response after induction, and toxicity were evaluated to define the more adequate up-front induction regimen in transplantation-eligible MM patients

Monocyte-to-HDL Ratio (MHR) Predicts Vitamin D Deficiency in Healthy and Metabolic Women: A Cross-Sectional Study in 1048 Subjects

Vitamin D deficiency is often linked with Metabolic Syndrome, both being more frequent with ageing and associated with an increase inflammatory state. Recently, monocytes-to-high density lipoprotein (HDL) ratio (MHR) has emerged as a powerful index to predict systemic inflammation. In this cross-sectional study, we investigated the association between circulating vitamin D level (25-OH vitamin D) and inflammatory status in a population of 1048 adult individuals. Our study reveals an inverse association between 25-OH vitamin D levels and MHR in the overall population. When the population is stratified by gender, waist circumference, and body mass index (BMI), we observed that while in men this relation is strongly significative only in condition of central obesity, in women a lifelong negative correlation exists between circulating 25-OH vitamin D and MHR and it is independent of the metabolic status. These observations underscore the relevance of circulating biomarkers such as MHR in the prediction of systemic inflammatory conditions sustained by vitamin D deficiency also in healthy and young women